An Introduction to Acids
By Hanna G.
October 31, 2018
Hailed as a wonder ingredient, acids claim to fame stem from its ability to fight acne, smoothen out fine lines, fade age spots and scarring, as well as even out skin tone. Phew.
We take a look at three popular acids – alpha-hydroxyl acid, salicylic acid and hyaluronic acid.
Alpha-Hydroxyl Acid (AHA)
AHAs are water-soluble acids loved for its ability to improve the texture and appearance of skin. AHAs can be derived synthetically or naturally from ingredients such as sugar cane (glycolic acid) and sour milk (lactic acid).
AHAs work to mildly flake off and expose new, underlying skin, making them gentle exfoliants.
Studies done on glycolic acid (the smallest size, highest penetrating AHA) have shown that creating acidic conditions within the skin cell stimulates receptors that allow calcium ions to flow into the cell. This process continues until an overload of calcium ions in the cell occurs resulting in cell death and skin exfoliation1.
Salicylic acid is often categorized as a beta hydroxy acid (BHA), but its chemical structure and function differ from other members of the beta hydroxy acid family such as malic acid and citric acid2.
Salicylic acid is synthetically produced or derived naturally from willow bark, for example. This oil-soluble acid can penetrate through sebaceous glands making it suitable for normal to oily skin.
Salicylic acid works to loosen the protein bonds between the cells, encouraging turnover of the skin. It also has anti-inflammatory effects and tests have shown that they are less irritating than AHAs3.
Hyaluronic acid (HA) is a naturally occurring polysaccharide (carbohydrate) known for its unique capability to retain water in the skin. It is a key component of connective tissue in our bodies, with the skin accounting for 50% of total body hyaluronic acid.
Sodium hyaluronate, the salty cousin of HA, is also commonly used in skincare and both names are used interchangeably. While they have similar functions, sodium hyaluronate is more popular because it is easier to formulate, more stable and cheaper.
HA has different molecule weights which affect its ability to absorb into the skin. High molecular weight HA sits on the skin surface and acts as an excellent humectant where it binds to water to maintain hydration. The lower the molecular weight, the deeper the HA penetrates to smoothen the skin surface and exhibit encouraging anti-wrinkle effects.
Interestingly, however, a study found that ultra-low molecular weight HA can trigger pro-inflammatory responses in the skin4,5. This is rarely used, if at all, since the primary function of HA in skincare is for moisture so high molecular weight HA is usually found.
1. Journal of Biological Chemistry. Intracellular Proton-mediated Activation of TRPV3 Channels Accounts for the Exfoliation Effect of α-Hydroxyl Acids on Keratinocytes
2. Clinical, Cosmetic and Investigational Dermatology. Applications of hydroxy acids: classification, mechanisms, and photoactivity
3. The Journal of Clinical and Aesthetic Dermatology. The Use of Lipohydroxy Acid in Skin Care and Acne Treatment
4. ACS Biomater Sci Eng. High and low molecular weight hyaluronic acid differentially influence macrophage activation
5. International Journal for Applied Science. Low Molecular Weight Hyaluronic Acid: Its Effects on Epidermal Gene Expression and Skin Ageing