The efficacy of AHAs is directly related to the amount of free acid present in the product. A low pH (pKa) means more free acid, and greater penetration into the dermis, but with a greater potential for adverse reactions. Many products are prepared with a high concentration of an AHA, but are "buffered" with an alkaline solution such as NaOH or NH4OH, decreasing the acidity (raising the pH) and irritation potential of the product. This is why some products containing as little as 2% AHA can be more effective (and more irritating!) than products containing 20% or even more AHA. As AHAs became a more popular ingredient in skin care products over the last decade, the incidence of adverse reactions seen with high concentrations, such as severe erythema, blistering, pigmentary changes and eye irritation, prompted the Cosmetic Ingredient Review Panel of the FDA to limit consumer products containing AHA's to a 10% or less concentration, and salon products to less than 30% concentration or pH 3.0 or higher. Physicians may use AHA's in higher concentrations and lower pH, either alone or in combination with other agents, as in a Jessner's peel.
Beta Hydroxy Acid (BHA): There is only one clinically important beta hydroxy acid, Salicylic Acid. This substance, a close relative of the common aspirin, is repelled by water and highly soluble in fats and oils, and is used primarily to open comedones and expedite penetration of less fat soluble AHAs into oily skin. It's most commonly used in combination with AHAs in light peeling solutions.
Retinoids: Retin-A (retinoic acid or tretinoin), originally approved for the treatment of acne, has been shown to be effective for the prevention and treatment of sun-induced skin aging. Effects include increased collagen and circulation in the upper or papillary dermis, reduction in hyperpigmentation and brown spots, increased cell turnover in the upper layers of skin, including blackheads and pores, and an overall improvement in the appearance of the skin. These beneficial effects of retinoids are related to the dose and duration of use, with the optimum effect noted after at least a year of treatment. Unfortunately, topical retinoids tend to be very irritating, with most patients experiencing redness, flaking, and increased skin sensitivity. Increased sensitivity to the sun is another drawback of retinoid therapy. A less well known drawback of retinoid therapy is that prolonged use (>4 months) is needed to produce significant improvement in the appearance of the skin. New and improved preparations of tretinoin, including Retin-A Micro and Renova, use improved delivery methods to minimize irritation.
Newer "Third Generation" topical retinoids, such as Differin (adapalene) and Tazorac and Avage (tazarotene) are currently approved for treatment of acne and photoaging. Avage (tazarotene) has been accepted as the "gold standard" topical retinoid for cosmetic use. Like other retinoids, it exerts its action on cellular receptors, and appears to be somewhat less irritating and photosensitizing, as well as more effective for both acne and photoaging, than Retin-A. Some of the effects of Avage include:
improvement of collagen synthesis and repair
decreased production and aggregation of melanosomes, thereby improving pigmentary abnormalities
increased production of ground substance (hyaluronic acid), thus "plumping" the skin and improving wrinkles
normalization of differentiation of keratinocyte differentiation, which decreases formation of clogged pores and scaly premalignant patches.
Retinoid activity is related to binding on nuclear retinoic acid receptors (RAR's) thereby regulating specific gene expression.
Like other retinoids, Avage needs to be properly incorporated into a skin care regimen to avoid unecessary irritation and maximize its effects. For more information on the proper use of Avage, click here.
Retinol: Vitamin A, or Retinol, is converted to retinoic acid (tretinoin, Retin-A) in living cells. When applied to skin, Retinol penetrates betterthan retinoic acid, and does not produce the same irritating effects. Although its clinical effects are not as dramatic as retinoic acid, retinol is available without prescription and has been incorporated into many skin care products. Regular exfoliation with AHAs may enhance the effects of Retinol.
