Salicylic acid is a colorless, crystalline organic carboxylic acid powder that melts at 159°C; it is soluble in ethanol and ether but is only slightly soluble in water.
Beta hydroxy acids (BHA) is a larger molecule than their cousin, alpha hydroxy acids. The larger molecule size keeps the beta hydroxy acid on the surface of the skin allowing it to more effectively penetrate and exfoliate within the pore. This action within the pores make it an ideal exfoliant for use on acne and acne-prone skin. The larger molecule size of salicylic acid produces less irritation than alpha hydroxy acids, making it a welcome alternative for those with sensitive skin. Salicylic Acid is best on acne-prone and sensitive skin types. The pore-cleansing properties of salicylic acid make it a more effective comedone fighter. Those with sensitive skin who cannot tolerate alpha hydroxy acids may find that they are able to use salicylic acid with good results. However, alpha hydroxy acid’s penetration into the deeper layers of the skin produce better anti-wrinkle and anti-aging benefits. BHA has the ability to penetrate into the pore (AHAs do not), and thus can exfoliate inside the pore as well on the surface of the skin; that makes it effective for reducing blemishes, including blackheads and whiteheads.
The typical use level for salicylic acid is 0.5-2%. A 1% concentration would be better or sensitive skin types and a 2% concentration would be useful on stubborn acne.
As an exfoliant, salicylic acid can actually increase the benefits of other therapies used in conjunction with it. However, care should be taken to watch for signs of excess irritation. If irritation occurs, then it would not be a good idea to continue combining therapies. For acne prone skin, retinol makes a good adjunct therapy for salicylic acid.
Make sure that you measure the pH value after adding salicylic acid as it can lower the pH significantly. A pH of lower than 3.5 should be avoided as skin irritations can occur. To avoid excess peeling/irritation of the skin be careful when using salicylic acid together with abrasive soaps or cleansers, alcohol-containing products, or other topical acne or peeling products (e.g. benzoyl peroxide, resorcinol, sulfur, tretinoin), soaps or cosmetics that dry the skin.