The Other Acids

When glycolic acid was introduced in the early 1990s, it was revolutionary for skincare. Known as an alpha-hydroxy acid (AHA), it was the first over-the-counter active ingredient you could use at home to accelerate cell turnover and reveal the fresher, smoother, plumper skin underneath. Later, we learned that the sugar cane derivative could also stimulate your skin’s collagen production. Then came salicylic acid, a beta-hydroxy acid (BHA) that could dissolve sebum build-up deep inside pores and act like an anti-inflammatory, making it good for red, irritated, acned skin. As a result, glycolic acid became the gold standard for anti-aging and salicylic acid became an anti-acne darling. That remained largely unchanged until recently. Now, some skincare products have lesser-known acids such as mandelic, phytic, tartaric and lactic. Why the additions? “I think of glycolic and salicylic acids as the lead actors in a play and these other acids as the supporting cast. When they all work together, they can improve the production,” says Shape Brain Trust member Dr Neal Schultz, a New York City dermatologist.

These supporting players improve efficacy for two reasons. First, while most acids aid in exfoliation, “each does at least one additional beneficial thing for the skin,” says NYC dermatologist Dr Dennis Gross. These include boosting hydration, fighting free radicals and helping to stabilise a formula so it lasts longer.

The second reason is that using multiple acids at a lower concentration (instead of one at a high concentration) may make a formula less irritating. “Rather than adding one acid at 20 per cent, I prefer to add four acids at 5 per cent to achieve similar results with less chance of causing redness,” says Dr Gross. So what specific benefits do these up-and-comers offer? We break it down:

MANDELIC ACID

This is an especially large molecule, so it does not penetrate the skin deeply. “That makes it better for sensitive types because shallower penetration means a lower risk of irritation,” Dr Gross says. Renee Rouleau, a celebrity aesthetician in Austin, says this AHA can also help “suppress the production of excess pigment”. With one caveat: “Mandelic acid helps improve exfoliation and lower the risk of irritation when combined with glycolic, lactic or salicylic acid, but it’s probably not enough of a power player to exist in a product alone.”

LACTIC ACID

It has been around for a long time – Cleopatra used spoiled milk in her baths around 40 BC because the milk’s natural lactic acid helped slough away rough skin – but has never achieved glycolic-level fame because it’s not quite as strong, which can be a good thing. Lactic acid is a large molecule, so it’s an effective alternative for sensitive types, and unlike mandelic acid, it’s potent enough to be a lead player in a product. Dr Gross explains that lactic acid also bonds to the top layer of skin and stimulates it to make ceramides, which help keep moisture in and irritants out.

MALIC ACID

Sourced primarily from apples, this AHA offers some of the same anti-aging benefits as lactic acid, but “it’s considerably more mild,” says Dr Debra Jaliman, a New York City dermatologist. When added as a supporting ingredient in a formula with stronger acids such as lactic, glycolic and salicylic, it aids gentle exfoliation and ceramide stimulation.

AZELAIC ACID

Neither an AHA nor a BHA, azelaic acid, derived from wheat, rye or barley, “has both antibacterial and anti-inflammatory properties, making it an effective treatment for acne or rosacea,” says Dr Jeremy Brauer, a New York dermatologist. It treats both by descending into follicles, killing any bacteria inside them and quelling the inflammation caused by infection. Azelaic acid can also inhibit the skin’s excess production of melanin, which is responsible for dark spots, freckles and uneven patches on the skin, says Dr Jaliman. It’s appropriate for darker skin (unlike hydroquinone and some lasers) because there’s no risk of hypopigmentation or hyperpigmentation, and it’s approved for pregnant and nursing women. That’s a huge plus because “so many women have issues with melasma and breakouts around pregnancy,” Dr Jaliman says.

PHYTIC ACID

Another acid that is neither an AHA nor a BHA, this outlier is an antioxidant, so it helps fend off skin-ageing free radicals. It can also prevent blackheads and shrink pores. “Phytic acid works by gobbling up calcium, which is notoriously bad for the skin,” Dr Gross says. “Calcium converts your skin’s oil from a fluid to a wax, and it’s the thicker wax that builds up inside pores, leading to blackheads and stretching out pores so they appear larger.”

TARTARIC ACID

This AHA comes from fermented grapes and is added to glycolic or lactic acid formulas to strengthen their sloughing. But its primary benefit is its ability to regulate a formula’s pH level. “Acids are notorious for morphing pHs, and if they swing too high or too low in a product, the result is skin irritation,” says Renee. “Tartaric acid can help keep things stable.”

CITRIC ACID

Similar to tartaric acid, citric acid, an AHA found primarily in lemons and limes, keeps other acids within a safe pH range. Additionally, it acts as a preservative, enabling skincare formulas to stay fresher for longer. Finally, citric acid is a chelator, which means it eliminates irritating impurities (from air, water and heavy metals) on the skin. “Citric acid grabs onto these impurities so that they cannot enter your skin,” Dr Gross says. “I like to think of it as skin’s Pac-Man.”