Skincare science: what is salicylic acid and how does it benefit oily skin?

A cursory glance at the skincare shelf in your nearest beauty hall throws up a mystifying number of ingredients ending in the word ‘acid’. But if you suffer from acne or an oily complexion blighted by blocked pores, you should reach for cleansers, toners and serums laced with salicylic acid, here's why.

“In the world of exfoliants, you will come across two classes of acid: beta-hydroxy acids (BHAs) and alpha-hydroxy acids (AHAs),” explains Martin Lyne, founder of Woods Copenhagen, which harnesses the power of salicylic acid in its new Skin Perfector 2% BHA. “Both AHAs and BHAs are chemical exfoliating agents, but AHAs are water-soluble, targeting the skin’s surface, while BHAs are oil-soluble, penetrating the skin more deeply.”

Salicylic acid falls under the BHA umbrella and is extracted from willow tree bark. Percentages of 0.5 to two per cent are usually gentle enough for at-home use.

Essentially, this silver bullet gently exfoliates and dissolves the oil, dirt and other unspeakables lurking inside your pores. So you can retire the grainy exfoliating scrubs, which only add to the trauma of already inflamed skin. But that’s not all.

“Salicylic acid also has anti-inflammatory and antibacterial properties,” says Lyne. “It works at pore level, which is where breakouts form, and penetrates the oil glands, effectively slowing down the skin’s natural oil production. This is why salicylic acid is a great ally for oily skin types and why it can often be found on the ingredient list of acne-fighting products.”

In other words, as well as preventing future breakouts by decongesting and neutralising bacteria within pores, salicylic acid treats existing spots and redness, too.

AHAs, such as glycolic acid or lactic acid, are ideal for treating the surface of your skin. But salicylic acid, crucially, is also lipophilic. “This means it is able to dissolve in oil and penetrate deep into the pores where it dissolves the sticky ‘glue’ that holds the sebum and dead skin cells together,” says Lyne. “Once these bonds are broken, the dead skin cells are shed, pores are unclogged and there is an improvement in skin texture as well as in whiteheads, blackheads, and small red pimples.”

Salicylic acid may sound innocuous but it still needs to be used correctly. According to Emelie Sundesten, head of product development at Caia Cosmetics, “salicylic acid works best on oily and acne-prone skin types.” That said, it’s best avoided if your acne-like bumps are a symptom of rosacea as your skin may be too reactive to tolerate it.

The key thing to be mindful of is that salicylic acid can be drying. “Although salicylic acid is considered safe overall, it may cause skin irritation when you first start using it,” Sundesten explains, adding that for this reason, Caia's Oil Control Day Cream is formulated with salicylic acid and panthenol to help counteract dehydration. “Acne treatments can be harsh on your skin, especially if you use multiple products containing salicylic acid all at the same time. So you want to avoid overusing this ingredient and removing too much oil as you may actually suffer more breakouts as a result.”

Sundesten advises applying salicylic acid three times a week and building up the usage to every day. There is one caveat, though. “In the summer months, when you know you'll be getting direct sun exposure, only apply salicylic acid at night and wear an SPF during the day,” she warns, if you want to get ahead of the clear-skin curve.