Dry Skin

Published on 15/03/2015 by admin

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Chapter 26 Dry Skin

Zoe Diana Draelos

Dry skin is an area where cosmeceuticals play an important role both in enhancing the efficacy of prescription medications and in preventing disease relapse. In a world where the medical and social benefits of cleansing are well recognized, dry skin can result both from endogenous and exogenous causes. No matter what the cause, the appearance, functioning, and feel of dry skin can be effectively improved through the use of cosmeceuticals. Table 26.1 organizes the cosmeceutical actives such that the dermatologist can select which ingredients might be most beneficial in a moisturizer for a given patient. The table has been broken into the subgroups of occlusives, humectants, stratum corneum modifiers, and emollients.

Table 26.1 Cosmeceutical actives for dry skin

Cosmeceutical Effects on skin physiology Patient selection comments
A: Occlusive moisturizing
Petrolatum Rapidly reduces transepidermal water loss (TEWL) by 99% Most effective for extremely dry skin, greasy, decreases scaling appearance
Mineral oil Reduces TEWL by approximately 40% Less greasy than petrolatum, does not cause acne
Lanolin Mimics human sebum Common cause of allergic contact dermatitis, not used in hypoallergenic formulations
Lanolin alcohol Similar to lanolin, but branched molecule provides smooth skin feel Excellent at smoothing skin surface, common cause of allergic contact dermatitis
Liquid paraffin Provides protective film, reduces TEWL Excellent hand and foot moisturizer for hand dermatitis and dyshidrosis
Carnauba wax Provides protective film somewhat thinner than liquid paraffin Same as liquid paraffin, naturally derived ingredient
Dimethicone Reduces TEWL without greasy feel Excellent for acne and sensitive skin patients, hypoallergenic, noncomedogenic, nonacnegenic
Cyclomethicone Thicker silicone than dimethicone Same as dimethicone
B: Humectant
Propylene glycol Attracts water from viable epidermis and dermis to stratum corneum Not good on abraded or sensitive skin as can cause stinging
Glycerin Most effective humectant available to increase stratum corneum hydration If used in too high concentration will create sticky feeling on skin, especially under high humidity conditions
Hyaluronic acid Used as a secondary humectant May be used to supplement glycerin to decrease stickiness
Panthenol Vitamin B5 is the most effective vitamin humectant May be used to supplement other humectants
Sodium PCA Considered part of natural moisturizing factor for skin May be used to supplement glycerin to decrease stickiness
C: Stratum corneum modifying
Ceramides Naturally present as part of intercellular lipids Improves skin barrier in atopic dermatitis
Cholesterol Naturally present as part of intracellular lipids Should be balanced with free fatty acids and ceramides
Urea Increases water binding sites on dehydrated keratinocytes Hydrates calluses and keratin debris
Lactic acid Decreases corneocyte adhesion Enhances desquamation of corneocytes in ichthyosis
D: Emollient
Cetyl stearate Smoothes desquamating corneocytes Most common emollient, nongreasy skin smoothing effect
Dicaprylyl maleate Used to dissolve UV sunscreens in moisturizing formulations Provides excellent smooth skin feel
C12–15 alkyl benzoate Fills in spaces between desquamating corneocytes Less waxy feel on skin than paraffin

A quality moisturizer should contain ingredients from each of the subgroups to improve the skin barrier through many different complementary mechanisms. The goals of moisturization are to increase skin water content, improve skin smoothness, and decrease symptoms of itching, stinging, and burning. The water content of the skin can be improved by retarding transepidermal water loss while increasing the flux of water from the dermis to the epidermis. The best agent at decreasing transepidermal water loss is petrolatum; however, it must be combined with silicone and mineral oil to decrease its stickiness. Water flux from the dermis to the epidermis is accomplished through the use of humectants; usually glycerin is used as the primary humectant in combination with a secondary agent. Finally, the skin must be made to appear smooth through the use of emollients that fill in the gaps between the desquamating corneocytes.

While all of the previously discussed ingredients are considered cosmeceuticals, the recent ability to artificially synthesize ceramide 3 has decreased the cost of this raw material such that it can now be used in facial moisturizers to speed barrier repair. Urea and lactic acid are also useful cosmeceuticals. Urea is unique in that it can open up the water binding sites on keratin, thereby hydrating dry, callused skin. This hydration of the hardened keratin allows for softening and easier removal of callus material and improved appearance of xerotic skin characterized by retained dehydrated keratinocytes. Lactic acid is also helpful in the treatment of xerosis and photoaged skin, since it dissolves the intercellular keratinocyte bridges encouraging desquamation.

Moisturizers are true cosmeceuticals. They have the ability to profoundly alter the structure and function of the skin. Their true main role is to enhance or maintain the water content of the skin, but they are also the most efficient vehicle for delivering sun protection and other actives. The majority of the unique actives discussed in this book are applied to the skin in some type of moisturizer. This is due to the fact that moisturizers are applied on a daily basis to the entire face, providing an ideal vehicle to transport the active to the face. Furthermore, moisturizers contain both water-soluble and oil-soluble ingredients into which either hydrophilic or lipophilic actives can be dissolved. For this reason, an understanding of moisturizers is key to understanding cosmeceuticals.

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