AHAs,BHAs, LHAs, and PHAs in Skincare

I do not think I need to spend too much time on this chapter. I feel this is the one area of Esthetics school where there is a good amount of focus. I am just going to do a brief run-down of the different chemical exfoliants and how they work. 

Alpha hydroxy acids (AHAs) are defined by Milady Standard Esthetics: Fundamentals (2012) as:

“Acids derived from plants (mostly fruit) that are often used to exfoliate the skin; mild acids; glycolic, lactic, malic, and tartaric acid. AHAs exfoliate by loosening the bonds between dead corneum cells and dissolving the intracellular matrix. Alpha hydroxy acids also stimulate cell renewal” (Page 723).

What this is telling us is that alpha hydroxy acids (derived either naturally or synthetically) break down the bonds between the skin cells, thus encouraging the sloughing off of these corneocytes. Doing so reveals younger more refined skin that appears much smoother, is more hydrated, and, over time, becomes visibly firmer.

AHA’s, Smallest to Largest

Glycolic acid: Comes from sugarcane and is the smallest AHA with the deepest penetration. Specifically known for its ability to retexturize skin.

Lactic acid: Found in foods that go through a bacterial fermentation process (sour milk, pickles, beer). Lactic acid is also a great moisturizing ingredient due to increasing the water-holding ability of the skin.

Malic acid: Found naturally occurring in apples and cherries, it is the third smallest of the AHA’s. I find this acid is rarely used by itself, but instead is found in conjunction with other AHA’s.

Tartaric acid: Found in red wine, it is also an antioxidant. This acid is more often used to stabilize the pH for other AHA’s.

Citric acid: From citrus fruits, this acid is typically used more as a pH adjuster in a product as opposed to an actual exfoliant. The pH of citric acid is around 2.2, which makes it very irritating to the skin in large percentages.

Mandelic acid: Derived from bitter almonds and is the largest of the AHA’s. This AHA is a good choice for sensitive and dry skin as the penetration of the product is limited and research has shown that this ingredient may increase sebum production.

On the other hand, we have beta hydroxy acids, which essentially refers to salicylic acid. The Milady Standard Esthetics: Fundamentals (2012) defines BHA’s as: “Beta hydroxy acids (BHAs), exfoliating organic acid; salicylic acid; milder than alpha hydroxy acids (AHAs). BHAs dissolve oil and are beneficial for oily skin” (page 725).

The last sentence of that definition is the most important part of BHAs. Due to its ability to dissolve oil, salicylic acid enters the pore, loosening the dead skin cells and oil that build up within the pore. Salicylic acid is derived from the willow bark or birch tree, which gives it antimicrobial and antiseptic benefits. 

Another great benefit of salicylic acid is its ability to calm and soothe irritated skin. PHAs or polyhydroxy acids are like AHAs in that they dissolve the bonds that hold the corneocytes together but are limited by their large size.

Examples of PHAs are gluconolactone, galactose, and lactobionic acid. PHAs are often found in skin care products in combination with AHAs as they work nicely together to exfoliate, brighten, and hydrate the skin.

LHAs or lipohydroxy acids work along the skin’s surface by detaching the bonds between individual corneocytes as well as decreasing the bacteria within the pores. LHAs are a much larger molecule then BHAS and AHAS, so it is well tolerated by sensitive skin. 

Within skin care products you may see LHAs listed as capryloyl salicylic acid as it is a derivative of salicylic acid. A great article by Dr. Joshua Zeichner discusses studies showing LHAs making a significant reduction in acne pustules and an improvement in skin tone and smoothness. LHAs have also been shown to increase collagen and elastin production like the use of tretinoin.

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