Alpha-hydroxy acids (AHAs) have a long history of use in dermatological preparations and recently have become important ingredients in cosmetics.
AHAs are organic carboxylic acids in which there is a hydroxy group at the two, or alpha carboxylic acids in which there is a hydroxy group at the two, or alpha [α] position of the carbon chain. Many are naturally occurring products. Glycolic Acid and Lactic Acid are two of the most commonly used AHAs in retailed cosmetic products.
Products containing AHAs are marketed for a variety of purposes, such as smoothing fine lines and surface wrinkles, improving skin texture and tone, unblocking and cleansing pores, and improving skin condition in general. Sometimes AHAs are used in cosmetics for other purposes, such as to adjust the pH (the degree of acidity or alkalinity).
AHAs reportedly cause an acceleration of cell turnover in the stratum corneum by peeling away the dead skin cells on the skin surface, revealing fresh new skin cells underneath. Specially at high concentrations, some concern has been expressed that the removal of dead skin surface cells may adversely affect the barrier function of the stratum corneum. Impairment in skin barrier function may have consequences on the skin.
Due to this mechanism of action, and despite their widespread use, the concern of these ingredients lies with
The maintenance of barrier function integrity of the skin including the effects on skin absorption of other cosmetic ingredients
The effects of AHA on skin’s responses to UV exposure
The evaluation of the safety of long-term use of AHA
The available data demonstrate that AHA ingredients can be dermal irritants. These data show an interdependence of concentration and pH. At a given pH, increasing the concentration increases irritation. At a given concentration, reducing the pH increases the irritation.
Taking each of these areas of concern into consideration (irritation, penetration enhancement, and sun sensitivity), it is considered that a limitation on both concentration and pH is appropriate for AHA ingredients.
However, even within those concentration, pH, and training constraints, it is possible to formulate in ways that would be inappropriate and, therefore, urged that products be formulated to limit irritation.
Furthermore, taking into regard the effects mentioned before, there are specific requirements for the labeling of cosmetic products containing these ingredients in order to inform and warn consumers.
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