Salicylic acid is an organic compound with the formula HOC6H4COOH. A colorless, bitter-tasting solid, it is a precursor to and a metabolite of aspirin (acetylsalicylic acid).

It is a plant hormone and has been listed by the EPA Toxic Substances Control Act (TSCA) Chemical Substance Inventory as an experimental teratogen. The name is from Latin salix, for willow tree. It is an ingredient in some anti-acne products. Salts and esters of salicylic acid are known as salicylates.

Salicylic acid-soaked cotton pads can be used to chemically exfoliate the skin. The outer layer of the skin is frequently removed with the use of the medicine salicylic acid. As a result, it is applied to treat ichthyosis, ringworm, psoriasis, acne vulgaris, and warts.Salicylic acid, like other hydroxy acids, is a common component in skincare products for the treatment of warts, calluses, keratosis pilaris, acanthosis nigricans, ichthyosis, and seborrheic dermatitis.

Salicylic acid is a bactericide, an antiseptic, and a food preservative that is used in manufacturing. Other medications, such as 4-aminosalicylic acid, sandulpiride, and landetimide (through salethamide), are made from salicylic acid. Acetylsalicylic acid, the active ingredient in aspirin, is made primarily from salicylic acid.Salicylic acid controls COX-1 enzyme activity to reduce the production of prostaglandins, which are pro-inflammatory. Salicylate may reduce prostaglandin synthesis through competition. Salicylate's analgesic and anti-inflammatory mechanisms are what give it its antirheumatic (nonsteroidal anti-inflammatory) effects.

When salicylic acid is applied to the skin's surface, the epidermis' cells slough off more easily, avoiding clogged pores and creating space for new cell development. Salicylic acid competes with nicotinamide adenine dinucleotide to prevent the oxidation of uridine-5-diphosphoglucose (UDPG), but not UDPG itself. Additionally, it hinders the transfer of the uridine-5-phosphoglucuronic acid's glucuronyl group to the phenolic acceptor by competitive means.Salicylates' ability to delay wound healing is most likely a result of their inhibition of the production of mucopolysaccharides.

In plants, salicylic acid can be found in free form as well as as carboxylated esters and phenolic glycosides. According to several studies, these plants contain salicylic acid, which humans may detectably metabolize.Beer, coffee, tea, several fruits and vegetables, sweet potatoes, almonds, and olive oil are examples of foods and drinks high in salicylates. Low salicylate content can be found in meat, poultry, fish, eggs, dairy products, sweets, breads, and cereals.A low-salicylate diet may be necessary for some people who are sensitive to dietary salicylates because they may experience allergic response symptoms such as bronchial asthma, rhinitis, gastrointestinal problems, or diarrhea.
High quantities of salicylic acid can enter the blood when vast areas of the body are covered in salicylic ointment, necessitating hemodialysis to prevent further issues.