Salicylic Acid

What is salicylic acid?

Salicylic acid is produced by plants to help defend against pathogen attack and environmental stress (R, R). It was first isolated from the willow in the 1830s, and first chemically synthesized in the 1870s (R, R). Dietary sources of salicylic acid include fruit, vegetables, tomato-based juices and sauces, fruit juice, tea, wine, and various herbs and spices (R).

Does salicylic acid get absorbed?

Salicylic acid readily penetrates healthy skin, especially on the cheek, neck and groin area but also on the breast, back, thigh, lower leg and the foot, though not the sole (R). It penetrates mainly through the transfollicular route (R). Skin in which the stratum corneum barrier has been perturbed due to damage by skin irritants or conditions such as psoriasis show even higher penetration of salicylic acid relative to intact, healthy skin (R, R). Repeated applications of salicylic acid at daily intervals increases its penetration flux as well (R).

The vehicle plays an important role in the topical delivery of salicylic acid, with absorptive ointments and collodion formulations delivering a greater amount of salicylic acid across intact skin (R, R, R). Hydrogels, a microgel, an oleogel and a transdermal patch containing salicylic acid and niacinamide have also been developed (R, R, R).

Other techniques that have been explored to enhance or control absorption include the prodrug strategy (R), a molecular form technique to prepare supersaturated solutions (R), iontophoresis (R, R), ion-pair formation (R, R) the use of different polymers as emulsifiers,(R, R, R) and the use of penetration enhancers (R).

What happens after salicylic acid is absorbed?

The mean plasma concentration of salicylic acid after application of a facial peel containing 30% salicylic acid for 5 minutes is 0.81 µg/ml and reaches a maximum of 56.4 µg/ml after 1.4 to 3.5 hours. These values are similar to that observed when a leave-on product containing 2% salicylic acid is applied (R). Systemically available salicylic acid is eventually eliminated through the urine (R).