an acid trip
If you’ve ever taken a chemistry class, you’ve probably heard about acids and pH. If you need a refresher, let’s take a little science trip together because not all acids are equal. Acids are incorporated into cosmetic and personal care products for various reasons. Choices can include adjusting the pH of the formula or to use as a cosmetic active.
What is an acid, and how is it relevant to pH?
An acid is a substance that can donate protons or accept a pair of valence electrons to form a bond. pH is a measure of the concentration of hydrogen ions or protons in a solution. In short, it measures how acidic or basic something is.
generic pH scale
higher concentration of hydrogen ions = acidic
lower concentration of hydrogen ions = basic
Acids in products for pH purposes
pH can play an important part in cosmetic and personal care products. If you’re interested in skin or hair care, you’ve probably heard that skin has a pH around 5.5 and hair around 4.5. It is a little more complex than this, but I will generalize it as correct for now because skin and hair care products are generally formulated in this range for that reason.
Acids can be used to adjust the pH of a formula downward to be more acidic. The most common acid to be used as a pH adjuster is citric acid, and this is why you will see it in many products.
As A Cosmetic Active - Chemical Exfoliation
When used as a cosmetic active, the most common benefit is exfoliation. Chemical exfoliation differs from physical exfoliation to help cells shed by using chemical exfoliants in comparison to a physical scrub or tool that uses friction. Chemical exfoliation will increase cell turnover, which can then improve overall skin texture, hyperpigmentation, or even target signs of aging.
Common exfoliation acids include alpha hydroxy acids (AHA), beta hydroxy acids (BHA), and poly hydroxy acids (PHA).
There is a trend to name products by including the main marketing ingredient in the name so consumers can find products easily based on ingredients. A few notable exfoliating example products that fall under this trend include:
If you’ve taken organic chemistry, you’ve probably heard about alpha and beta positions, as well as hydroxy acid. The term “hydroxy” indicates an -OH group or an alcohol. The term “acid” indicates a carboxylic acid. Alpha and beta positions are determine by the number of carbon(s) apart the alcohol and carboxylic acid group are from each other.
AHAs and BHAs differ in structure and in solubility. AHAs are water soluble, and BHAs are oil soluble. BHAs are considered the superior choice for those with oily or acne-prone skin because it is oil soluble. PHAs have a similar effect to AHAs but have been found to be less irritating in comparison.
Common AHAs
Glycolic acid
Lactic acid
Malic acid
Mandelic acid
Citric acid
Common BHA
Salicylic acid (an OTC active ingredient for acne)
Common PHA
Lactobionic acid
Gluconolactone
As A Cosmetic Active - Other
Acids other than the typical AHA, BHA, and PHA exfoliating acids can smooth texture, brighten, or provide other cosmetics benefits like hydration. These can include:
Hyaluronic acid - an anionic polysaccharide (large sugar molecule) that occurs in various tissues and is well known for water retention
Kojic acid - tyrosinase inhibitor that inhibits melanin production, inhibits melanocyte activation, can also mildly exfoliate skin
Azelaic acid - a saturated dicarboxylic acid, prevents tyrosine conversion to melanin, anti-inflammatory properties (can also be an annoying ingredient to formulate with)
Tranexamic acid - prevents melanocyte activation
A few notable example products that fall under this “other” category include:
Conclusion
Always remember to patch test any product before use, especially an acid. Overexfoliation is counterproductive and can disrupt your skin barrier, so take it slow by exfoliating once a week first. When acids are used safely and correctly, you can really reap the best benefits.