The AHA (alpha-hydroxy acids), BHA (beta-hydroxy acids) and PHA (poly-hydroxy acids) are chemical exfoliants to adopt for achieving radiant and smooth skin. However, to avoid any skin discomfort, it is appropriate to choose the right acid according to your skin type. Find some answers to this topic in this article.
AHA, BHA and PHA: Which one to choose?
Summary
Published on October 24, 2024, by Maylis, Chemical Engineer — 5 min of reading
Themes:
The AHA (alpha-hydroxy acids).
The AHA, or alpha-hydroxy acids, are water-soluble acids. They are generally recommended for dry skin as they exfoliate the surface while keeping the epidermis hydrated. In skincare, there are several types of AHA.
Theglycolic acid, derived from sugarcane, is renowned for its exfoliating power on the upper layers of the epidermis, as well as for its astringent and deep-cleansing virtues. It also has a moisturising power due to its stimulating effect on cell renewal and the synthesis of hyaluronic acid.
Thelactic acid is derived from the fermentation of milk and certain fruits. In addition to its keratolytic properties, researchers have shown that it improves skin hydration. Due to its larger molecular weight compared to glycolic acid, the lactic acid remains on the skin's surface. This superficial action allows it to exfoliate and hydrate the skin without causing irritation. Furthermore, it is a molecule naturally present in the skin as it is part of the Natural Moisturising Factor (NMF).
Themandelic acid originates from almonds. This active ingredient also has antibacterial and anti-inflammatory properties, making it particularly recommended for blemished skin.
BHA (Beta Hydroxy Acids) for combination to oily skin types.
In comparison to AHA, BHA works on the skin's surface and within the pores. In skincare, the main BHA used is salicylic acid, a fat-soluble acid. This active ingredient, originally extracted from willow bark, has interesting properties for the care of oily skin prone to imperfections. Thanks to its antiseptic action, it prevents the growth and proliferation of fungi, viruses, and bacteria, such as Cutibacterium acnes, a microorganism responsible for the inflammatory reactions of acne.
It also exerts akeratolytic action and purifying effect. It promotes the removal of dead cells on the surface of the epidermis and stimulates cellular renewal. Furthermore, itssoothing virtues help to reducesymptoms related to inflammation. Salicylic acid plays a role in the arachidonic acid cascade and inhibits the synthesis of prostaglandins E2, molecules responsible for inflammatory and painful effects. In the treatment of acne, it thus soothes painful spots and visibly reduces redness. Finally, itssebum-regulating properties target the formation of comedones and prevent the clogging of pores that leads to blackheads.
PHAs for sensitive skin.
Sensitive and reactive skin requires gentle exfoliation. With a larger molecular size than AHA and BHA, the PHA. penetrate less deeply into the epidermis and are more suitable for atopic skin and/or skin with cutaneous afflictions.
The three main PHAs used in cosmetics are the gluconolactone, an antioxidant that effectively fights against inflammation; the galactose, which stimulates the production of collagen and thelactobionic acid known for its hydrating properties.
Sources
SMITH W. P. Epidermal and dermal effects of topical lactic acid. Journal of the American Academy of Dermatology (1996).
HEARING V. J. & al. Applications of hydroxy acids : classification, mechanisms, and photoactivity. Clinical Cosmetic and Investigational Dermatology (2010).
ARIF T. Salicylic acid as a peeling agent: a comprehensive review. Clinical, Cosmetic and Investigational Dermatology (2015).
ROTSZTEJN H. & al. Lactic and lactobionic acids as typically moisturizing compounds. International Journal of Dermatology (2019).
