Cosmetics and Cosmeceuticals

Cleansers

The development of soaps designed to cleanse the skin has been the single most important advance in decreasing disease worldwide. Even though soap is ubiquitous in the developed world, one of the main goals of global health organizations is to introduce the concept of cleansing with soap to regions of the world where contagious diseases run rampant. In basic chemical terms, soap is a fatty acid salt resulting from a reaction between a fat and an alkali . The soap solubilizes sebum and environmental dirt, such that it can be rinsed away with water. The mechanics of rubbing the soap over the skin with the hand or a bathing implement results in the physical removal of desquamating scales, bacteria and fungi from the skin surface. In high-income countries, where bathing has become a daily ritual, excessive use of soap has resulted in dermatologic conditions such as xerotic eczema. This has led to the development of cleansers with skin conditioning benefits that are chemically not true soaps, and they are referred to as detergents.

Cleansers, whether formulated as bars or liquids, can be divided into three basic types: soaps, syndets and combars ( Table 153.1 ). True soaps are composed of long-chain fatty acid alkali salts with a pH of between 9 and 10. This alkaline pH raises the pH of the skin following cleansing, resulting in stratum corneum barrier disruption and the resultant feeling of tightness following bathing. Alkalinization of the skin disrupts the natural acid mantle, which may be significant in dermatitic skin. Recognition of the need to preserve skin pH at 5.4 led to the development of syn thetic det ergents, known as syndets, such as sodium cocoyl isethionate. Syndet cleansers, also known as beauty cleansers, contain less than 10% soap and are designed with a pH of 5.5–7.0 in order to minimize cutaneous alkalinization . The third type of cleanser, known as a combar, is composed of an alkaline soap to which surface active agents with a pH of 9–10 have been added. Combars are milder cleansers than true soaps, but induce more thorough cleansing than syndets. For example, true soap is a good cleansing choice for excessively oily or dirty skin, while a combar is a good cleanser for normal skin with a moderate amount of environmental dirt. Syndets would be the least damaging to the cutaneous barrier in persons with xerosis or any form of dermatitis.

The many brands of cleansers currently on the market fall into one of the three aforementioned groups, yet there must be something unique, for marketing purposes, about each cleanser. The unique aspects of each cleanser are created through the addition of specialty additives ( Table 153.2 ). Common cleanser additives include various fragrances as well as foaming agents designed to alter the aesthetics of the lather, but the most dermatologically relevant additives are antibacterial agents. The most widely used antibacterial in both bar and liquid cleansers used to be triclosan , but is now benzalkonium chloride. Triclosan works by blocking lipid synthesis within the bacterial cell wall, thus decreasing the skin biofilm bacteria count and reducing odor. However, in 2016, triclosan was banned in the US as an ingredient in consumer antiseptic washes.

Another important dermatologic need with regard to skin cleansing is minimization of skin barrier dysfunction. Unfortunately, surfactants cannot distinguish unwanted sebum and oil-soluble dirt from intercellular lipids. Thus, increases in transepidermal water loss are typically noted in direct proportion to the cleansing ability of the cleanser. An attempt to provide cleansing and barrier restoration in the same product has led to the development of body washes. Since body washes are liquids, incorporating both hydrophilic and lipophilic ingredients emulsified into a single phase, it is possible to cleanse and moisturize simultaneously while allowing for rinsing away of the surfactants. Body washes must be used with a puff to introduce both water and air into the cleanser emulsion in sufficient quantity to allow cleansing and moisturization to occur. The syndet detergents, primarily ammonium laureth sulfate, solubilize oil-soluble dirt into the rinse water for removal during the cleansing phase when the body wash concentration is high and the water concentration low, while occlusive moisturizing substances (e.g. petrolatum) and emollients (e.g. soybean oil) are left behind to retard transepidermal water loss and improve skin smoothness during the rinse phase when the body wash concentration is low and the water concentration is high.

Other cleanser variants for persons with dry, dermatitic skin include lipid-free, non-foaming cleansers and cold creams. These products are excellent at removing cosmetics and low levels of environmental dirt. Lipid-free cleansers are non-foaming, soap-free liquid products applied to dry or moistened skin, rubbed to produce minimal lather, and rinsed or wiped away. They possess low surfactant capabilities, and they can only remove bacteria through mechanical means, yet they are important in persons with barrier disruption . The classic cleanser for dry, dermatitic skin is cold cream, which combines the effect of a lipid solvent, such as wax or mineral oil, with detergent action from borax . However, not all formulations of cold creams contain borax.

Occasionally, a dermatologic need arises for specialty cleansers designed to offer a skin benefit beyond pure removal of sebum and environmental dirt. For example, it may be desirable to induce corneocyte disadhesion in older patients requiring an exfoliant cleanser. This can be accomplished through the addition of chemical exfoliants, such as salicylic acid or glycolic acid, to the cleanser formulations discussed previously. Exfoliant cleansers containing benzoyl peroxide or salicylic acid are sometimes used as an adjunct in topical acne treatment. Exfoliation can also be induced mechanically through the incorporation of fine abrasive particles (such as polyethylene beads, aluminum oxide, ground fruit pits, or sodium tetraborate decahydrate granules) in a liquid syndet cleanser to remove skin scale. Lastly, mechanical exfoliation can be encouraged through the use of specially woven face cloths, designed to remove skin scale without inducing epidermal damage.

The development of novel detergents and cleansing specialty additives has created a confusing plethora of consumer products, yet the goal remains the same: to allow adequate skin hygiene without barrier damage. Our next concern is the discussion of moisturizers, designed to replace skin sebum and natural moisturizing factors in instances where the stratum corneum barrier has been damaged from exuberant cleansing.

Moisturizers

The term “moisturizer” is somewhat misleading to the consumer, who assumes that the cream or lotion actually puts moisture or water back into the skin . Moisturizers do not put water back into the skin externally, nor do they get incorporated into the intracellular lipids. Moisturizers simply attempt to retard transepidermal water loss and create an optimal environment for restoration of the stratum corneum barrier . The optimal water content for the stratum corneum is between 10% and 30%, depending on the measurement technique employed, and moisturizers can function to raise the cutaneous water content through occlusion or humectancy via a variety of active agents ( Table 153.3 ) .

Occlusive moisturizers prevent evaporative water loss to the environment by placing an oily substance on the skin surface through which water cannot penetrate, thus replenishing the stratum corneum moisture by water movement from the lower viable epidermal and dermal layers . There are many different classes of chemicals that can function as occlusive moisturizers , for example, hydrocarbon oils and waxes (petrolatum, mineral oil, paraffin, squalene), silicones (cyclomethicone, dimethicone), vegetable oils (castor oil, corn oil, grape seed oil, soybean oil), animal oils (mink oil, emu oil), fatty acids (lanolin acid, stearic acid), fatty alcohols (lanolin alcohol, cetyl alcohol), polyhydric alcohols (propylene glycol), wax esters (lanolin, beeswax, stearyl stearate), vege­table waxes (carnauba wax, candelilla wax), phospholipids (lecithin), and sterols (cholesterol, ceramides) .

The most effective occlusive moisturizer is petrolatum, since it reduces transepidermal water loss by 99% . Total occlusion of the stratum corneum is undesirable, since transepidermal water loss is the cellular signal that initiates barrier repair and the resulting synthesis of intercellular lipids . Complete cessation of transepidermal water loss results in no barrier repair, allowing water loss to return to its pretreatment level once the complete occlusion has been removed . Petrolatum allows barrier repair while permeating throughout the interstices of the stratum corneum .

Another technique for rehydrating the stratum corneum is the use of humectants. Humectants are substances that attract moisture; they include glycerin, honey, sodium lactate, urea, propylene glycol, sorbitol, pyrrolidone carboxylic acid, gelatin, hyaluronic acid, and some vitamins and proteins . The body utilizes hyaluronic acid and other glycosaminoglycans in the dermis as biologic humectants to prevent desiccation of the skin. Humectants can only hydrate the skin from the environment when the ambient humidity exceeds 70%. Consequently, rehydration of the stratum corneum generally occurs by water that is attracted from the deeper epidermal and dermal tissues. Most moisturizers combine both occlusive and humectant moisturizing ingredients, since water drawn by a humectant to a damaged stratum corneum barrier will be lost to the atmosphere unless trapped by an occlusive . Humectants also help to improve the smoothness of xerotic skin by inducing corneocyte swelling and minimizing voids between the desquamating corneocytes .

In summary, remoisturization of the skin must occur in four steps:

• initiation of barrier repair (see Ch. 124 )

• alteration of surface cutaneous moisture partition coefficient

• onset of dermal–epidermal moisture diffusion

• synthesis of intercellular lipids .

Moisturizers attempt to increase stratum corneum water content through the principles of occlusion and humectancy. The discovery of aquaporin 3 channels in the skin and their modulation by glycerin and urea has increased research into osmotic cell balance as another mechanism for moisturization.

Astringents

Occasionally, patients use skin care products that either correct the deficiencies of the cleanser or supplement the effects of the moisturizer. These products are known as astringents or toners (see Table 153.1 ). They are used after cleansing but before moisturizing, and they are left on the face following use. Astringents are usually liquids wiped over the face with a cotton ball. Originally, astringents were intended to remove soap scum left behind on the face from the use of lye-based soaps and hard water. If left behind, this soap scum could cause irritant contact dermatitis. The original astringents were fragranced isopropyl alcohol or propylene glycol solutions designed to remove oil-soluble residue. The development of synthetic detergents and treated water has made this original intent obsolete, yet astringents remain popular.

Currently, astringents are used to remove the oily residue left behind after cleansing of the face with lipid-free cleansers or cleansing creams, discussed previously. Oily complexion astringents are formulated to remove any remaining sebum from the face following synthetic detergent cleansing or to deliver keratolytics, such as salicylic acid, glycolic acid or witch hazel. Some astringents designed for dry skin contain a humectant liquid moisturizer, such as propylene glycol or glycerin, and skin soothing agents, such as allantoin, guaiazulene or quaternium-19 . A complete cosmetic-counter facial treatment routine involves a cleanser followed by an astringent and then a moisturizer. Once the skin has been prepared in this manner, colored cosmetics are applied.

Facial foundations