Salicylic Acid

Salicylic acid is one of the golden oldies of skincare. It is a peeling and anti-inflammatory agent with several indications, including acne vulgaris, melasma, photodamage, freckles, dandruff, thick cracking skin, and warts.

It is a white crystalline powder with a faint chemical smell. It is soluble in oils rather than water (unlike AHAs) and belongs to the group of beta-hydroxy acids (BHAs).

It works by breaking down the junctions that connect the cells in the topmost layer of skin, as well as interacting with the lipids fused with them, resulting in the softening, loosening, and eventual peeling of the dead skin cell layers, including the lining of skin pores.

Salicylic acid has different effects depending on its concentration. In low concentrations (0,5 - 2%) it is gently exfoliating and soothing, suitable for the treatment of acne, comedones/blackheads, post-acne redness, and hyperpigmentation.

Higher concentrations (up to 10%) are used for disorders where there is an increased production of dead skin - psoriasis, keratosis, or ichthyosis. Concentrations above 10% can be found in wart-treating pastes and chemical peels.

In more sensitive individuals and especially in high concentrations, salicylic acid can produce side effects like burning, redness, allergic reactions, or skin dryness.

Whereas AHA peels are generally considered safe even for pregnant and breastfeeding women, salicylic acid is different. It is readily absorbed through the skin and into the bloodstream and can harm an unborn baby's development. It is dangerous for newborns and toddlers and should be avoided during pregnancy and breastfeeding.

Salicylic acid peelings should not be used alongside some dermatologic medications, such as topical retinoids or topical benzoyl peroxide. These should be discontinued at least a few days before the peeling.

Ingredients that work well with salicylic acid include glycolic acid (the anti-acne effects are enhanced in combination treatment), niacinamide (the sebum-reducing and pore size reducing effects are enhanced in the combination treatment), and vitamin C (both work best in an acidic pH).

It is better to have a skincare product that already combines them in a stabilized formula. If you mix the different products on your own, you may overshoot the concentrations or create imbalances in the pH and formulation which may render your active ingredients, well…inactive.

Salicylic acid is often compared to benzoyl peroxide for the treatment of acne. For the most part, they produce similar results (antibacterial, comedolytic, and sebostatic effects) but the mechanism of action is different: salicylic acid breaks down the junctions between the cells, whereas benzoyl peroxide breaks down keratin.

Salicylic acid has direct anti-inflammatory action and benzoyl peroxide kills bacteria by its oxidative properties. Lastly, benzoyl peroxide is much more irritating and often produces redness and burning, even in low doses.

Azelaic acid, another effective acne treatment ingredient, may produce very similar results, but it has a very different mechanism of action. It is mainly an antibacterial and anti-inflammatory substance and doesn't act as an exfoliant, but instead decreases the production of new keratin. It also has tyrosinase activity which makes it a direct anti-pigment ingredient.