Salicylic acid plays a vital role within some species of plants, serving as a chemical messenger or hormone. Without salicylic acid, these plants would be unable to produce their own food through photosynthesis, eliminate excess water and transport nutrients to their leaves and flowers. In its natural, isolated state, salicylic acid consists of tiny, clear crystals.
The original source for salicylic acid was the bark of trees from the Salix genus or willow family. The herb meadowsweet was also once used for extracting salicylic acid. For modern day use, salicylic acid is made in a laboratory by exposing the amino acid phenylalanine to a series of chemical reactions. In labs, salicylic acid can also be produced by removing hydrogen atoms from the water molecules found in ordinary aspirin.
The use of salicylic acid as a medicinal ingredient can be traced back to the writings of the ancient Greek doctor Hippocrates, which were completed during the 5th century BC. The physician originally used the bark from the willow tree to eliminate fevers and pain. Salicylic acid was also used by the Native Americans in North America for similar purposes. Formal scientific research began on the acid during the 19th century when it was discovered to be a part of a group of organic chemicals known as beta hydroxy acids.
The investigation of the use of salicylic acid for skin care did not occur until the 20th century, and the FDA did not fully evaluate the use of the ingredient for over-the-counter facial exfoliators until 2000. The FDA now lists salicylic acid as "Generally Regarded as Safe", but some people with sensitive skin experience redness and swelling from the use of the ingredient. Although pregnant women should consult their doctors before using any type of skin care product, salicylic acid is not known to pose risks to fetuses and can be used as a treatment for children.
Salicylic acid is widely used in over-the-counter skin care products in 2 to 6 percent concentrations. For some medical conditions, prescription strength formulas over 6 percent in strength are available. Side effects are more likely with stronger formulations of the ingredient.
Perhaps the most well known use of salicylic acid is in acne treatment products. Salicylic acid weakens the bonds that hold older skin cells to newly produced skin cells, allowing the older tissue to be shed from the complexion. For acne sufferers, eliminating dead skin helps to prevent clogs that cause acne papules and blackheads. It can also be beneficial for those suffering from deep acne cysts. As an added benefit, salicylic acid is a mild antibacterial, which enables it to kill some of the bacteria that contribute to the infections that occur inside of the pores and lead to the formation of acne blemishes.
The exfoliative properties of salicylic acid also make it ideal for treating other skin care conditions. The ingredient is often found in creams, lotions and serums that help to shrink enlarged pores. For those with stretched, visible pores, salicylic acid eliminates blockages and prevents new clogs from occurring. Salicylic acid can also be effective at evening out the texture of skin tissue that is marked by acne scars.
The ability of salicylic acid to resurface the complexion makes it a useful ingredient in anti-aging skin care products. When used in wrinkle creams and serums, the ingredient helps to make fine lines and wrinkles less apparent, smoothing the surface. Salicylic acid can also be employed in formulas that treat skin discoloration like age spots and melasma.
In shampoo form, salicylic acid is often used to treat dandruff and seborrheic dermatitis. The exfoliative action of the ingredient allows it to loosen the flakes that form on the scalp, and when the hair is rinsed, these particles are washed away. In addition, salicylic acid has been shown to normalize oil levels in the skin tissue, which helps to decrease the greasy, shiny appearance of the scalp that often occurs with seborrheic dermatitis.
A common clinical use for salicylic acid is in the treatment of warts. Doctors often apply salicylic acid dressings to these growths, as the ingredient is capable of dissolving them. Some over-the-counter wart removal products also contain low doses of salicylic acid.