Pyramid Middle: Renewal
(Moisturization, Exfoliation, and Cell Turnover)
The next layer of the skin pyramid is the middle and encompasses moisturization, exfoliation, and cell turnover. Here we have moved beyond the stratum corneum and viable epidermis into the epidermis and superficial dermis. Moisturization is the basis of the pyramid middle, since the basic mechanism of action for many cosmeceuticals is to enhance skin water content thereby reducing fine lines of dehydration. While moisturizing ingredients are typically the basis for the vehicle in most cosmeceutical products, the vehicle here is an important active. Moisturizers function by decreasing transepidermal water loss (TEWL) by placing a water-resistant coating over the skin surface. This can be accomplished with occlusive agents, such as petrolatum, lanolin, shea butter, waxes, silicones, mineral oil, vegetable oils, etc. Reducing TEWL creates an environment for barrier repair allowing the skin to restore natural water balance; however, in low humidity conditions under 40%, water will continue to be lost to the environment. Thus, moisturizers must also contain humectants that draw water from the dermis to the epidermis and possibly from the environment, but the humidity must exceed 70%. Humectants draw water, but the skin barrier must retain the water, otherwise TEWL will increase and accelerate skin dehydration.
The water content in the skin is assessed by a technique known as corneometry. Here a capacitive sensor is used to measure the permittivity of upper skin layers, which correlates with skin hydration. Substances that can increase skin water measurements act like sponges and mimic the natural humectants in the dermis, which are glycosaminoglycans. The most widely recognized glycosaminoglycan is hyaluronic acid, originally cross-linked and developed as an injectable facial filler, but now synthetically available in topical cosmeceuticals. Other humectants include sodium PCA, glycerin, sorbitol, urea, sodium lactate, propylene glycol, butylene glycol, honey, etc. Well-formulated cosmeceutical moisturizers include both occlusive and humectant ingredients to combine both mechanisms of remoisturization. In summary, the goals of a moisturizer are: 1) to increase skin hydration, 2) to make the skin feel smooth and soft, 3) to deliver cosmeceutical actives to the skin, and 4) to improve skin appearance.
Rough scaly skin can possess an excellent skin barrier with adequate water content, but still appear dry and unattractive. This may be due to a desquamatory failure. The enzymes that provide for skin exfoliation require a moist environment for activity, thus moisturization may also encourage desquamation; however, desquamation can be enhanced by the topical application of alpha hydroxy acids (AHAs). AHAs are a group of organic carboxylic acids distinguished by a substituted hydroxy group covalently bonded to the α-carbon of a carboxylic acid.13 AHAs, such as glycolic acid, lactic acid, and malic acid, can disrupt the ionic bonding at the level of the stratum granulosum allowing the skin cells to slough.14,15 The epidermal effects of AHAs are a thinned stratum corneum with epidermal acanthosis and decreased melanogenesis while the dermal effects of AHAs are increased synthesis of glycosaminoglycans and increased dermal thickness.16,17
This is in contrast to salicylic acid, a lipophilic acid also used for effective exfoliation in the oily areas of the face and in the sebum laden pores. Salicylic acid appears to eliminate the stratum corneum layer by layer from the outermost level downward.18 This is in contrast to AHAs, which appear to diminish cellular cohesion between the corneocytes at the lowest levels of the stratum corneum.19 This difference is probably due to the watersoluble characteristics of the AHAs, which readily penetrate into the stratum corneum, and the oil-soluble characteristics of salicylic acid, which remains on the stratum corneum. Exfoliation, in combination with moisturization, is extremely effective in smoothing the skin surface and improving skin texture, which patients notice as increased radiance and luminosity. Too much aggressive exfoliation can damage the skin barrier and decrease water content, thus the two activities must balance one another.
Retinoids represent another important cosmeceutical ingredient category capable of producing receptor specific effects including regulating growth of epidermal cells and promoting differentiation of cell lines.20 The retinoid family includes retinol, retinyl esters, retinoic acid, retinyl palmitate, and retinsphere technology. Retinyl palmitate is the most stable of the vitamin A esters, however it is not very biologically active. Cosmeceutical activity of retinyl palmitate is thought to occur by cutaneous enzymatic cleavage of the ester bond and subsequent conversion of retinol to retinoic acid. Retinol, another common cosmeceutical retinoid is more readily converted to retinoic acid, but only small amounts of retinol can be converted by the skin.21 Retinsphere is the combination of two retinoids: a retinoic acid ester, hydroxypinacolone retinoate, and retinol in glycospheres or microsponges. This combination offers more chemical stability and improves retinol efficacy. Treatment tolerance with this combination is very high and does not cause the irritation often observed with other retinoids.22-24
Pyramid Top: Activation and Regeneration
We have now arrived at the top of the pyramid, which is characterized by dermal benefits to include dermal activation and regeneration. A variety of new cosmeceutical technologies have attempted to optimize skin from the inside including peptides, growth factors, stem cells, and circadian rhythm modifiers.
Peptides form the building blocks for proteins and are composed of amino acids, usually representing fragments of biologically active proteins. Peptides can be added to topical formulations to allow receptor modulation, activate enzyme release, or regulate protein production. The 3 families of peptides currently marketed
(Moisturization, Exfoliation, and Cell Turnover)
The next layer of the skin pyramid is the middle and encompasses moisturization, exfoliation, and cell turnover. Here we have moved beyond the stratum corneum and viable epidermis into the epidermis and superficial dermis. Moisturization is the basis of the pyramid middle, since the basic mechanism of action for many cosmeceuticals is to enhance skin water content thereby reducing fine lines of dehydration. While moisturizing ingredients are typically the basis for the vehicle in most cosmeceutical products, the vehicle here is an important active. Moisturizers function by decreasing transepidermal water loss (TEWL) by placing a water-resistant coating over the skin surface. This can be accomplished with occlusive agents, such as petrolatum, lanolin, shea butter, waxes, silicones, mineral oil, vegetable oils, etc. Reducing TEWL creates an environment for barrier repair allowing the skin to restore natural water balance; however, in low humidity conditions under 40%, water will continue to be lost to the environment. Thus, moisturizers must also contain humectants that draw water from the dermis to the epidermis and possibly from the environment, but the humidity must exceed 70%. Humectants draw water, but the skin barrier must retain the water, otherwise TEWL will increase and accelerate skin dehydration.
The water content in the skin is assessed by a technique known as corneometry. Here a capacitive sensor is used to measure the permittivity of upper skin layers, which correlates with skin hydration. Substances that can increase skin water measurements act like sponges and mimic the natural humectants in the dermis, which are glycosaminoglycans. The most widely recognized glycosaminoglycan is hyaluronic acid, originally cross-linked and developed as an injectable facial filler, but now synthetically available in topical cosmeceuticals. Other humectants include sodium PCA, glycerin, sorbitol, urea, sodium lactate, propylene glycol, butylene glycol, honey, etc. Well-formulated cosmeceutical moisturizers include both occlusive and humectant ingredients to combine both mechanisms of remoisturization. In summary, the goals of a moisturizer are: 1) to increase skin hydration, 2) to make the skin feel smooth and soft, 3) to deliver cosmeceutical actives to the skin, and 4) to improve skin appearance.
Rough scaly skin can possess an excellent skin barrier with adequate water content, but still appear dry and unattractive. This may be due to a desquamatory failure. The enzymes that provide for skin exfoliation require a moist environment for activity, thus moisturization may also encourage desquamation; however, desquamation can be enhanced by the topical application of alpha hydroxy acids (AHAs). AHAs are a group of organic carboxylic acids distinguished by a substituted hydroxy group covalently bonded to the α-carbon of a carboxylic acid.13 AHAs, such as glycolic acid, lactic acid, and malic acid, can disrupt the ionic bonding at the level of the stratum granulosum allowing the skin cells to slough.14,15 The epidermal effects of AHAs are a thinned stratum corneum with epidermal acanthosis and decreased melanogenesis while the dermal effects of AHAs are increased synthesis of glycosaminoglycans and increased dermal thickness.16,17
This is in contrast to salicylic acid, a lipophilic acid also used for effective exfoliation in the oily areas of the face and in the sebum laden pores. Salicylic acid appears to eliminate the stratum corneum layer by layer from the outermost level downward.18 This is in contrast to AHAs, which appear to diminish cellular cohesion between the corneocytes at the lowest levels of the stratum corneum.19 This difference is probably due to the watersoluble characteristics of the AHAs, which readily penetrate into the stratum corneum, and the oil-soluble characteristics of salicylic acid, which remains on the stratum corneum. Exfoliation, in combination with moisturization, is extremely effective in smoothing the skin surface and improving skin texture, which patients notice as increased radiance and luminosity. Too much aggressive exfoliation can damage the skin barrier and decrease water content, thus the two activities must balance one another.
Retinoids represent another important cosmeceutical ingredient category capable of producing receptor specific effects including regulating growth of epidermal cells and promoting differentiation of cell lines.20 The retinoid family includes retinol, retinyl esters, retinoic acid, retinyl palmitate, and retinsphere technology. Retinyl palmitate is the most stable of the vitamin A esters, however it is not very biologically active. Cosmeceutical activity of retinyl palmitate is thought to occur by cutaneous enzymatic cleavage of the ester bond and subsequent conversion of retinol to retinoic acid. Retinol, another common cosmeceutical retinoid is more readily converted to retinoic acid, but only small amounts of retinol can be converted by the skin.21 Retinsphere is the combination of two retinoids: a retinoic acid ester, hydroxypinacolone retinoate, and retinol in glycospheres or microsponges. This combination offers more chemical stability and improves retinol efficacy. Treatment tolerance with this combination is very high and does not cause the irritation often observed with other retinoids.22-24
Pyramid Top: Activation and Regeneration
We have now arrived at the top of the pyramid, which is characterized by dermal benefits to include dermal activation and regeneration. A variety of new cosmeceutical technologies have attempted to optimize skin from the inside including peptides, growth factors, stem cells, and circadian rhythm modifiers.
Peptides form the building blocks for proteins and are composed of amino acids, usually representing fragments of biologically active proteins. Peptides can be added to topical formulations to allow receptor modulation, activate enzyme release, or regulate protein production. The 3 families of peptides currently marketed
