Development Team
Principal Investigator Prof. Farhan J Ahmad Jamia Hamdard, New Delhi
Paper Coordinator Dr. Javed Ali
Jamia Hamdard, New Delhi
Content Writer
Dr. Jasjeet Kaur Narang
Department of Pharmaceutics, Khalsa College of Pharmacy, Khalsa University, Amritsar
Content Reviewer Prof. Alka Ahuja
Oman Mediacl College, Muscat
CONTENTS
Biphasic liquid preparations:- Emulsions- Introduction, types of emulsion, identification tests of emulsion preparations, preparation of emulsions, stability of emulsions.
Suspensions- Selection of wetting, suspending and dispersing agents, preparation of suspensions, stability of suspensions.
Creams- Introduction, types of creams, stability of biphasic liquid formulations and creams.
Lotions- Introduction, types of lotions, preparation of lotions and stability of lotions
Introduction
Now-a-days, aging of the skin is the most common problem in the human population.
Both intrinsic molecules (e.g. reactive oxygen species (ROS) and environmental factors (e.g. ultraviolet radiation) are responsible for the alteration in skin appearance and function. Wrinkles, uneven pigmentation and skin atrophy are indicative of individual’s aging. Due to these changes, an individual also suffers a decrease in social comfort and self-confidence.
In the manufacturing market of skin care products, topical applications in the form of emulsions, suspensions, lotions and creams (e.g. sunscreens), which help in rejuvenation of the aging skin, along with anti-oxidants properties which retard aging, are gaining importance.
1. Biphasic liquid preparations
Biphasic liquid preparations are composed of two phases which can either be both liquids resulting in formation of emulsions or one phase can be solid dispersed in liquid, thereby resulting in formation of suspensions.
1.1 EMULSION
Emulsions are widely used in cosmetics. An emulsion is a dispersion or thermodynamically unstable biphasic liquid preparation consisting of at least two immiscible liquids in which the dispersed phase is composed of small globules of liquid distributed in the other liquid phase stabilized by third substance called emulsifying agent. The function of the emulsifying agent is to form a film around the globules in order to scatter them indefinitely in the continuous phase, so that a stable emulsion is formed.
An emulsion system mainly consists of:
A dispersed liquid, known as the Internal or Discontinuous phase.
A dispersion medium, known as External or Continuous phase.
Stabilization is the main target in formulating emulsions because all emulsions suffer from separation.The selection of oils and emulsifiers determine the product form, appearance and viscosity of emulsions.
Types of Emulsions
1. Oil in Water type (o/w): In this, the oil is in dispersed phase whereas water is in the continuous phase. These have droplet size between 0.2-50 mm. These are preferred generally for internal use. The examples of emulsifying agents used for formulation of these types of emulsions are- methyl cellulose, gum acacia, synthetic substance, tragacanth etc.
2. Water in Oil type (w/o): In this type of emulsion, the water is in dispersed phase and oil is in continuous phase. These have droplet size between 0.01-0.2mm. The examples of emulsifying agents used in formulation of these types of systems are- resins, wool fat, beeswax etc. These are mainly used externally as lotions or creams.
The different types of emulsions are given in Figure 1.
w/o emulsion o/w emulsion
3. Multiple emulsion: They are the complex polydispersed systems in which both o/w and w/o emulsions exist simultaneously and are stabilized by lipophilic and hydrophilic surfactants respectively. The ratio of these surfactants is important in achieving stable multiple emulsion. These systems are also known as double emulsions. These can be either o/w/o or w/o/w.
4. Microemulsion: This is a biphasic system consisting of oil and water which is thermodynamically stable, optically transparent and stabilized by surfactants and
Lipophilic phase Hydrophilic
phase Emulsifying
agent
Homogenisation
Lipophilic phase (oil) Hydrophilic phase (water)
Homogenizer
Figure 1: Different types of emulsions
Hydrophilic phase Lipophilic phase
cosurfactants like Sodium Lauryl Sulphate (SLS). Figure 2 represents a typical structure of a microemulsion.
Figure 2: Microemulsion
Identification tests of emulsion preparation
The tests used to distinguish the o/w and w/o emulsions are given in Table 1.
Table 1: Identification tests of different types of emulsions S
No.
Tests Oil-in-water emulsions Water-in-oil emulsions 1 Miscibility tests:- Miscible with water but
immiscible with oil
Immiscible with water but miscible with oil
2 Dye test:- Scarlet red dye is used
a) Macroscopic examination
b) Microscopic examination
Paler colour than a w/o emulsion
Coloured globules on a colourless background
More intense colouration than with an o/w emulsion Colourless globules against a coloured background
3 Conductivity test:- Pair of electrodes connected to battery are dipped in both emulsions through a low voltage bulb
If bulb glows, the emulsion is o/w type because water is in the continuous phase.
If bulb does not glow, the emulsion is w/o type, because oil is in the continuous phase.
4 Fluoroscene test:- Certain oils exhibit physical property of fluorescing in the presence of ultraviolet radiation on microscopic examination.
If droplets show
fluorescence, it indicates that oil is present in disperse phase i.e o/w type emulsion
If the whole field shows fluorescences, it indicates that oil is present in
continuous phase i.e. w/o type emulsion.
5 Cobalt Chloride test:- A filter paper dipped in cobalt chloride is soaked in an emulsion
o/w emulsion results in change of colour from blue to pink
No such colour change is there
Preparation of emulsion
The selection of oil phase, water phase and emulsifying agent is an important criteria for the preparation of a stable emulsion.
Selection of oil phase
The selection of oil phase is important for the preparation of stable emulsions. Various oils are used for preparation of emulsions for both internal as well as external applications. A few of which include castor oil, cod liver oil, arachis oil, turpentine oil, benzyl benzoate, etc.
The emulsions used for the external purpose contain oils that are present as vehicle for the active agent. It is an important parameter that affects both the viscosity as well as transport of drug into the skin. Most widely used oil for the external application is liquid paraffin. However other examples include hard paraffin, soft paraffin, and light liquid paraffin. Although these oils result in the easy spreadability of formulation but at the time also produce sufficiently viscous, coherent film over the skin. Various waxes like beeswax, carnauba wax or higher fatty alcohols also play an important role in film forming. Continuous films are sufficiently tough and flexible to prevent contact between the skin and aqueous based irritant. These preparations are called barrier creams and many are of w/o variety.
Many of the oils are prone to oxidation. Therefore, it is necessary to add suitable anti oxidant agents like BHT, BHA in the formulation.
The selection of oil phase is determined by several factors which include:
a) Desired physical properties of the product b) Consistency of the product
c) Solubility of active product in the oil
d) Any possible incompatibilities
e) Potential toxicity of oil to the route of administration
Selection of aqueous phase
The selection of aqueous phase is determined by its pH which depends upon the skin sensitivity and nature of absorption. Mostly water is used. Optimum volume of aqueous phase should be decided for formulation of stable emulsion.
Selection of an emulsifying agent
Selection of an emulsifying agent is based upon the intended use of the emulsion formulated that is, whether it is to be used externally or internally. In case of external use, both ionic and non ionic emulsifying agents are added but in case of internal use, non-ionic and water soluble emulsifying agents are employed, since they are less irritant and less toxic. Also the selection of emulsifying agent is based upon the HLB value. Each surfactant is allocated an HLB number representing the relative proportion of lipophilic and hydrophilic parts of molecule.
Some of the examples of emulsifying agents with their HLB values are given in Table 2.
Table 2: Examples of emulsifying agents
Emulsifying agent HLB Value
Tween 20 16.7
Tween 80 15.0
Oleic acid 4.3
Span 60 4.7
Sodium Lauryl Sulphate (SLS) 40
Span 20 8.6
It is better to avoid the emulsifying agent of natural origin as they are more prone to microbial growth as well as to batch-to-batch variation.
The methods used for the preparation of emulsions are given in Figure 3.
Figure 3: Different methods for preparation of emulsions
1. Continental (Dry Gum, or 4:2:1) Method
This method is used to prepare the initial or primary emulsion from oil, water and a hydrocolloid or gum type emulsifier (usually acacia). This form of emulsion is formed from 4 parts oil, 2 parts water and 1 part emulsifier. Therefore, 4 parts oil and 11 part emulsifier represent the total amount for the final emulsion.
In this method, the oil is first triturated with gum with little amount of water to form the primary emulsion. The trituration is continued till a characteristic “clicking” sound is heard and a thick white cream is formed. Once the primary emulsion is formed, the remaining quantity of water is slowly added to form the final emulsion.
Solid substances (eg. active ingredients, preservatives, color, etc) are dissolved as a solution form to the primary emulsion. Oil soluble substance may be incorporated directly into the primary emulsion. After the incorporation of all ingredients, the emulsion is transferred to a calibrated vessel, brought to final volume with water, and finally homogenized or blended to ensure uniform distribution of ingredients.
2. English (Wet Gum) Method
In this method, the proportions of oil, water and emulsifier are same (4:2:1) but the order or technique is different. In this, 1 part gum is triturated with 2 parts water to form a mucilage; then 4 parts of oil are added slowly, in portion while triturating. After the complete addition of oil, the mixture is triturated for several minutes to form the primary emulsion. Generally this method is difficult to utilise with viscous oils, but if employed results in more stable emulsion.
3. Bottle (Forbes) Method
This method is used to prepare emulsion containing volatile oils and substances having very low viscosities. It is not recommended for viscous oils as it is difficult to agitate in bottle. In this method, one part powdered acacia (or other gum) is placed in a dry bottle
and 4 parts oil are added. The bottle is capped and thoroughly shaken. To this, the required volume of water is added all at once, and the mixture is shaken thoroughly until the primary emulsion forms. It is important to minimize the initial amount of time the gum and oil are mixed. Since the gum will tend to imbibe the oil, and will become more waterproof. The method is used for the preparation of an olive oil and lime water emulsion, which is self emulsifying.
4. Beaker Method
This method is used to prepare the emulsion by using synthetic or non-gum emulsifier by dividing the components into water soluble and oil soluble components. Both phases are heated to a temperature of 70° C over a water bath. The internal phase is then added to external phase with stirring until the product reaches room temperature. Mixing of such type of emulsion is carried out in beaker, mortar or in case of creams and ointments, in the jar in which they are dispensed.
5. Hand homogenizer Method
It is hand operated equipment in which coarse emulsion is passed through a fine orifice.
The emulsion preparation is placed in the hopper and the up and down movement of handle of the homogenizer causes emulsion to be draw through inlet and pass through orifice to get dispersed droplets size of about 5 microns or less.
Eg:- Silverson mixer homogenizer: It consists of an emulsifier head which is covered with fine meshed stainless steel sieve. The head consists of a number of blades rotated (by using electric motor) at high speed in order to produce a powerful shearing action.
The head is placed in a vessel containing immiscible liquids. When motor is started, the liquids are sucked through fine holes and oil is reduced into fine globules due to rotation of blades. An emulsion of fine particle size is formed which is then expelled out through the head.
Stability of emulsions
A stable emulsion is a one in which the dispersed phase retains its initial character and remains uniformly distributed throughout the continuous phase during its storage besides being free form bacterial growth during its shelf-life.
The various types of deviations from ideal stable behavior of emulsions resulting in instability in emulsions are given in Figure 4:-
INSTABILITY
Coalescence Creaming
Figure 4: Instability problems of Emulsion
Stable o/w emulsion
Phase inversion(w/o emulsion)
1. Cracking: Cracking of an emulsion system is due to the coalescence of dispersed phase globules which are difficult to redisperse by shaking.
It can be due to:-
a) Addition of emulsifying agent of opposite type: Soaps of divalent metals produce w/o type emulsion whereas soaps of monovalent metals produce o/w type emulsions. But if the addition of monovalent metals to divalent soap emulsion and divalent metals to monovalent soap emulsion is done, it leads to the cracking of emulsion.
b) Decomposition or precipitation of emulsifying agents: When acid is added to an alkali soap emulsion or vice versa, it leads to the decomposition and precipitation of emulsifying agent and thus cracking of emulsion takes place.
c) Presence of microorganisms: There may be a chance of bacterial and mould growth if emulsions are not stored properly. This may lead to destruction of an emulsifying agent resulting in cracking of emulsion. Therefore, if these systems are required to be stored for a long period then these should be suitably preserved.
d) Change in temperature: An increase in temperature results in reduction of viscosity, thereby encouraging creaming.
Avoidance of cracking
In case of o/w emulsion system, the coalescence of oil globules is resisted by the presence of a mechanically strong adsorbed layer of emulsifier around each globule.
This is achieved by the presence of either multimolecular film of a hydrophilic material or condensed monolayer of lipophilic and hydrophilic emulgents.
In case of w/o emulsion system, the presence of long, cohesive hydrocarbon chains projecting into the oil phase will prevent coalescence.
2. Creaming: It results in the separation of an emulsion into two regions in which there is an upward movement of dispersed globules to form a thick layer at the surface of emulsion. Example: creaming of milk. Creaming is however pharmaceutically undesirable and inelegant and if not shaken adequately, there is a risk of patient obtaining an incorrect dosage.
Creaming of an emulsion should be avoided because it may lead to cracking along with complete separation of two phases.
Avoidance of creaming Creaming can be avoided by:-
a) Formulation of small droplet size emulsion
This factor usually depends on the method of manufacture. The rate of creaming is directly proportional to the radius of the globules. As the size of globule increases, the creaming of emulsion increases. Therefore, in order to reduce the creaming of the emulsion, the droplet size should be reduced.
b) Reduction in the density difference between two phases
The rate of creaming generally depends upon the density difference of both phases.
Greater the difference in the densities of both phases, the more will be the creaming.
c) Control of dispersion phase concentration
The rate of creaming is inversely proportional to the viscosity of the dispersion medium. Therefore, a higher dispersed phase concentration would result in hindrance of movement of droplets thereby resulting in reduction in rate of creaming.
3. Phase inversion: The change of one type of emulsion in other type i.e o/w type emulsion changes to w/o type emulsion and viceversa, is known as phase inversion.
It may be due to the change in temperature, by changing emulsifying agent etc.
Avoidance of phase inversion
It can be minimized by keeping the concentration of disperse phase between 30 to 60%, storing the emulsion in a cool place and by adding appropriate and adequate concentration of emulsifying agent.
1.2 Suspension
Suspensions are the heterogeneous mixtures in which solid particles (internal phase or dispersed phase) are dispersed throughout the fluid (external phase or dispersion medium) by means of mechanical agitation, and use of various excipients or suspending agents. The size of solid particles ranges from 0.5 to 5.0 micron.
The particle size is a very important factor for the formulation of suspensions. In case of external preparations, the suspension meant for the skin care purposes should have small particle size in order to avoid gritty feeling to the skin and to cover a greater area of the application. For example: Lotion containing suspended particles evaporates when applied to the skin leaving a light deposit of medicament on the surface. Calamine lotion is a suspension type preparation which is applied on the skin to provide protective effect.
The suspension should be free from harmful microorganisms also.
Suspensions can be classified as flocculated and deflocculated suspensions. The difference between the two is given in Table 3.
Table 3: Difference between flocculated and deflocculated suspensions S. No. Flocculated suspension Deflocculated suspension 1 Particles form net-work like
structure due to loose aggregates
In this type of suspension particles exist as separate entities
2 Rate of sedimentation is high Rate of sedimentation is low
3 Sediment is rapidly formed and easy to be dispersed
Sediment is slowly formed and difficult to redisperse
4 Supernatant liquid is clear Supernatant liquid is not clear 5 Sediment is loosely packed and
does not form a hard cake
Closley packed sediment, resulting in the formation of a hard cake
6 Floccules stick to the side of bottle
No such stickiness of floccules is observed
7 Non-pleasing in appearance Pleasing in appearance 8 Bioavailability is high due to large
surface area
Bioavailability is low due to small surface area
9
Selection of wetting, suspending and dispersing agents Wetting agent
Wetting agents are surfactants that lower the interfacial tension and contact angle between solid particles and liquid vehicle. The usual concentration of surfactant varies from 0.05 to 0.5% and depends on the solids content intended for suspension. On the other hand, employing surfactants at conc. less than 0.05% results in incomplete wetting whereas at concentrations greater than 0.5%, surfactants solubilize ultra-fine particles and lead eventually to changes in particle size distribution and crystal growth.
Polysorbate-80 is still the most widely used surfactant for suspension formulation
because of its lack of toxicity and compatibility with most formulation ingredients. The rate of wetting is often determined by placing measured amount of powder on the undisturbed surface of water containing a given concentration of surfactant and measuring the time required to completely wet and sink the powder.
Suspending agent
These are the lipophobic (Hydrophilic) colloids, resulting in the formation of colloidal dispersion with water resulting in an increase in the viscosity of the continuous phase.
They act by forming film around particles thereby causing a decrease in interparticle attraction.
Suspending agents help active pharmaceutical ingredients to stay suspended in the formulation and prevent caking at the bottom of the container. A well formulated suspension with good suspending agent should be able to easily suspend by the use of moderate agitation or shaking.
Characteristics of ideal suspending agent
The characteristics of an ideal suspending agent are:-
(i) It should produce a high viscosity at negligible shear; i.e. during shelf storage; and it should result in a low viscosity at high shear rates, i.e. it should be free flowing during agitation, pouring and spreading on the skin.
Pseudoplastic substances e.g. tragacanth, sodium alginate and sodium carboxymethylcellulose show these desirable qualities and produce shear thinning systems in which when shaken or agitated the viscosity diminishes.
A suspending agent that is thixotropic as well as pseudoplastic proves to be useful since it forms gel on standing and becomes fluid when disturbed. E.g.: Bentonite and Carboxymethylcellulose have both pseudoplastic and thixotropic behavior.
(ii) Suspending agents should coat the particles and thus make them less prone to caking than the uncoated particles.
Examples of suspending agents used for formulation of suspension include
• Alginates
• Carboxymethylcellulose and its derivatives
• Microcrystalline cellulose
• Acacia
• Tragacanth
• Xanthan gum
• Bentonite
• Carbomer
Dispersing agent (Dispersant)
An agent either surface active or non surface active polymer which is added to suspension (colloid) for the purpose of preventing settling or clumping and to improve the separation of particles is known as dispersing agent.
Dispersing proceeds in three steps:
• Wetting of pigment agglomerates
• Deagglomeration of pigment agglomerates
• Stabilization of the resulting dispersion against flocculation
Preparation of suspensions
During preparation of suspensions following points are important and should be considered.
1. Selection of right materials that go into the manufacture 2. Steps involved and the sequence
3. Preservation and storage of the product
The following steps are involved in the preparation of suspension a) Size reduction of powder
The proper particle size of the powder can be obtained by using different equipments:
Ball mill Hammer mill Micropulverizer Spray dryer Mortar & pestle
Fluid energy of jet mill
b) The pharmaceutical powder with appropriate particle size is then wetted thoroughly with some amount of water miscible solvent.
c) Then suitable suspending agents with other ingredients are added to some amount of vehicle and added to above solution to form slurry
d) The slurry is then transferred to measuring cylinder.
e) The volume of the dispersion is made up.
Stability of suspensions
In the stability of suspensions, studies of various parameters like sedimentation volume, particle size, zeta potential and viscosity are important. The various tests conducted for assessing the stability of suspensions are:-
1. Assessment of sedimentation volume: In order to evaluate the stability of suspensions, the measurement of the sedimentation volume is important.
Procedure: It is determined by keeping a known volume of suspension in a graduated measuring cylinder in an undisturbed position for a definite period of time and noting the ultimate height (Hu) of the sediment and the initial height of total suspension (Figure 5). Thus, sedimentation volume, F is the ratio of ultimate height to initial height (Hu/Ho). A stable suspension shows a horizontal or less steep curve when a graph is plotted between sedimentation volume v/s time.
Figure 5: Sedimentation Method
1. Assessment of rheological parameters: The rheological parameters are evaluated at different time intervals with the help of a suitable viscometer, eg:- Brookfield viscometer.
2. Assessment of micromeritic parameters: The particle size plays an important role for the stability of the suspension because if the particle size increases, it may lead to the formation of lumps or cracking. Any change in particle size affects the stability of suspension. Microscopy and coulter counter are the methods for studying the changes in the size of particle as well as crystal habit of suspension with time which can in turn give an idea about the stability of product during storage.
3. Assessment of electrokinetic parameters: The determination of zeta potential or surface charge is helpful in order to determine the stability of suspension. Zeta potential can be calculated from the migration of the particles measured by electrophoretic method. Zeta potential is the difference between the shear plane and the electroneutral region of the solution in dispersion. It is the work done to bring a unit charge from infinity to the surface of the particle.
2. Creams
Creams are the skin care cosmetics that are intended to be rubbed or applied to the human body, or any other part for cleansing, beautifying, promoting attractiveness or altering the appearance. These have a unique composition that can alter the ability of
ingredients to reach the skin surface which also influences product esthetics. The sensory characteristics of creams are determined by the oily components, emulsifiers, polymers, product form and viscosity.
Types of creams
Creams are generally emulsions of either o/w or w/o types.
Depending upon the main ingredients and the purpose of these formulations, they are classified as:
A) Make up creams (o/w emulsion) 1.Vanishing Creams
2.Foundation Creams
B) Cleansing Cream (w/o emulsion)
C) Creams for Winter (w/o emulsion) 1. Cold Cream
D) Creams for dry skin
1. Moisturising Creams (and lotions) E) All purpose Creams
F) Night Creams
G) Skin protective and Hand Creams
A) Make up creams
Vanishing creams: These are o/w emulsions consisting of pearly stearic acid and spread on the skin (chiefly face) as a very thin, oil-less film which is not visible thus justifying the name vanishing cream. These are generally applied to skin as foundation creams to hold face powder and improve adhesion. The stearic acid is quite universal and most important ingredient for making vanishing cream.
The consistency of vanishing cream is governed by the amount of stearic acid saponified or neutralised and also by the alkali used.
Humectants are the second most important ingredients of the vanishing cream. Glycerin is the most widely used humectant. Propylene glycol and sorbitol are other humectants used in the formulation of vanishing cream. Vanishing creams also contain emulsifying agents such as TEA-soap and amino glycol soap.
Preservatives are also another important ingredients included in vanishing creams especially if they contain ingredients that are likely to deteriorate under bacterial or fungal infection. Methyl and propyl parabens are the preferred preservatives.
The emollients such as lanolin, cocoa butter etc. are also used in the preparation of vanishing creams.
An example of composition of a vanishing cream is given below:-
Stearic acid 17%
Lanolin 1%
Glycerin 6%
Water 71%
Alcohol 4.5%
Perfume 0.5%
Foundation creams: These creams unlike vanishing creams, usually contain pigments ground into these creams with a roll paint or an ointment mill.
The following ingredients are generally present in these creams:- 1. Oil phase:- Mineral oils, stearic acid
2. Emulgents:-SLS- 1%, Isopropyl myristate, etc.
3. Suspending agents:- Cellulose derivatives, Bentonite, etc.
4. Humectants:- Glycerine 5. Perfumes
6. Pigments: TiO2 and various colors.
7. Preservatives
B) Cleansing cream
Cleansing of skin with water alone is not adequate since the dirt on the skin which may consist either of residues of skin secretions or deposits from surrounding is bound by oily substances, which make it very adherent and difficult to remove. These types of creams contain water and are rubbed on the skin in a thin layer. The water they contain is to a large extent lost by evaporation, thereby leading to phase resulting in formation of w/o type emulsion in which solvent action on the binding oil is facilitated.
An ideal cleansing cream should possess the following characters:- 1. Should liquify at body temperature
2. Should be an emulsion type with less quantity of water
3. Should leave skin smooth, relaxed, refreshed, non-greasy and clean
4. Should penetrate the epidermis and contain enough light oils to permit flushing of pores
5. Should contain no such chemicals that are quickly absorbed by skin
Mineral oil is the essential ingredient of all cleansing creams. It is used in combination with other materials, resulting in the preparation that can easily and conveniently be applied to the skin and has an attractive appearance.
Generally cleansing creams are of two types:- Liquefying creams (absence of water)
Emulsified creams (presence of large proportion of oil)
Example: Noxzema Classic Clean (original deep cleansing cream)
C) Cold creams for winter
The term ‘cold’ is derived from the cooling sensation caused by evaporation of water in the cream after application to skin. It is one of the oldest preparations in cosmetics.
These are w/o emulsions usually containing beeswax and alkali. The newer type of cold creams developed in comparison to old ones which are prepared by the combination with absorption bases, emulsifying waxes or other additives.
Example of composition of a typical cold cream is:- White Beeswax 20%
Light mineral oil 58%
Borax 0.2%
Distilled water 20%
Perfume 1.8%
Method of preparation: Melt beeswax in waterbath at 70°C with the addition of light mineral oil. In another beaker, heat water to about 60-70°C and dissolve borax in it. Mix the aqueous phase and oily phase with proper stirring until a creamy emulsion is prepared. Add perfume.
D) Creams for dry skin
Dry skin can range from itchy skin lacking moisture to a geriatric hyper keratosis.
Vitamins and urea have found regular use in the formulation of creams for dry skin.
The correct approach for the treatment of dry skin should involve investigation of fundamental reasons for the cause of dryness, and preparing of specific products for each different condition and for different skin types. In addition to environmental factors, biological factors like ageing, hormonal disturbances etc also play a significant role in skin drying.
E) All purpose creams
These types of creams have combined properties of any cleansing cream, or cold cream. From the manufacturing point of view, any good cold cream or cleansing cream is assigned additional or extended use to designate it as an all purpose cream.
F) Night creams
These types of creams are usually applied at night for the better emollient effect. They act by supplying oils and fatty materials which are lacking in the usual dry skin. For better results, these are applied and left over night. The active ingredient may be either of vegetable or animal origin which can be easily absorbed by skin and has a softening effect.
Example: Lard oil and Lard are the animal origin products commonly used. Cocoa butter is another example which is readily absorbed and is light in color. Other ingredients used as emollient and hardening agents are Spermaceti, Cetyl alcohol etc.
Preservatives are also added in the animal origin formulations to prevent bacterial decomposition. E.g.:- PABA.
G) Skin protective and hand creams
These category of creams possess both beautifying as well as protective property.
These types of creams are helpful in preventing skin injuries from the changes in weather as well as act as industrial skin protectives. In industries, the workers have to use the skin protective products throughout the day to have protection against both the absorption and irritation from chemicals.
The ideal skin protectives should possess definite characteristics which include a) It should easily spread
b) It should provide an oil film of low surface tension c) Should not be dehydrating
d) Should be easy to remove without use of scrub or detergent
Besides the above mentioned category of creams, a number of other creams which include sunscreen Creams, anti acne creams and skin tonics and astringents are also in demand now days.
The sunscreen creams are intended to prevent the individuals skin from harmful effects of ultra violet rays.
Anti acne creams are loaded with therapeutic agents effective against acne. Tea tree oil, clove oil and salicylic acid are common ingredients of anti acne creams.
Skin tonics are widely prescribed by dermatologists for freshening the skin after cleansing. Tincture of benzoin, alcohol, camphor, borax, perfumes such as rose are common ingredients of skin tonics. Besides refreshing the skin they are also reported to relax the muscles by removing fatigue.
Astringent creams are used for their cooling and skin tightening effect.
Stability of biphasic liquid formulation and creams
The stability problems and their avoidance are discussed above under the heading of
“Stability of emulsion”.
3. Lotions
These are the low viscosity preparations applied to unbroken skin with bare hands, or a brush, or a clean cloth etc. These are intended to provide smoothness to skin, moisturize and soften it. Figure 6 represents the different types of lotions.
Figure 6: Different types of lotions
Types of lotions
1. Bath Lotion: After taking shower, these types of lotions are applied to whole body. These act by retaining skin’s essential oils that are lost after a warm shower or bath. These also replenish skin’s moisture and leave the skin irresistibly touchable.
2. Milk Bath: Milk baths are added during bath to nourish the skin.
3. Body Lotion: It is essential to apply daily to keep skin looking fresh and healthier by means of moisturizer. Extra body lotion has to be applied to areas such as knees, feet, elbows.
4. Baby Lotion: These lotions are intended for the sensitive skin as these are dermatologically approved and are free from harsh chemicals.
5. Hand Lotion: These lotions have special use for the hands which might always be in contact with harsh chemicals and other substances leading to dryness and dehydration. A hand lotion provides fast relief and nutrients in order to retain the morphology of the skin of hand.
6. Astringent Lotion: This is used to remove excessive oiliness on the skin, which is usually caused by eating greasy or oily foods.
Preparation of lotions
All lotion preparations contain the following ingredients:-
a) Aqueous phase: This is the base of the lotion, which makes it fluid and easily spreadable therefore resulting in better absorption into the skin.
b) Oily phase: It helps in sealing the skin’s moisture by forming a gentle layer on the skin. It is the main ‘moisture’ component of the lotion.
c) An emulgent: This is helpful in retaining the oil and water phase together, thus stabilizing the lotion.
d) Other ingredients: It may include antioxidants, preservatives, fragrances, dyes etc.
Stability of lotion
As the lotions are the biphasic system, the stability will be same as for emulsions and suspensions as discussed above under the title “Stability of emulsion”.
Summary
For the cosmetic skin care products, emulsions and suspensions are the best delivery systems as they offer both therapeutic as well as cosmetic uses. Therapeutically, they are the carriers for the delivery of drug at the site of action. In case of cosmetics, these have been used for the formulation of various cosmetic products like creams, cold creams, liniments, lotions of various categories, etc. Various emulsifying agents and suspending agents are used for emulsion and suspension formulations in order to stabilize these formulations for long term use. These formulations help in maintaining the skin’s natural integrity, and protect the skin from various diseases when used therapeutically. They are also used for beautifying purpose like foundation creams.
Overall, these biphasic systems are the best vehicles for the skin care.
