Safety
Topically, as a beta-hydroxy acid (and unlike alpha-hydroxy acids) salicylic acid is capable of penetrating and breaking-down fats and lipids, making it capable of causing moderate chemical burns of the skin if at very high concentrations (such as near or actually the majority ingredient) within a solvent. It is capable of damaging the lining of pores in such cases if the solvent is alcohol, acetone, or an oil. Over-the-counter limits are set at 2% for topical left on the face and 3% for those expected to be washed off, such as acne cleansers or shampoo. Caution should be exercised when handling large volumes of salicylic acid, and protective gloves are recommended for any repeat, prolonged exposure. 17% salicylic acid, which is often sold for wart removal, should not be applied to the face and should not be used for acne treatment. Even for wart removal, such a solution should only be applied twice a day – more frequent use may lead to an increase in side effects without an increase in efficacy.
When ingested, salicylic acid has a possible ototoxic effect by inhibiting prestin. It can induce transient hearing loss in zinc-deficient individuals. This finding is based on clinical studies with rats. An injection of salicylic acid induced hearing loss in zinc-deficient rats, while a simultaneous injection of zinc reversed the hearing loss. An injection of magnesium in the zinc-deficient rats did not reverse the salicylic acid-induced hearing loss.
There are no studies specifically looking at topical salicylic acid in pregnancy. Oral salicylic acid has not been associated with an increase in malformations if used during the first trimester, but use in late pregnancy has been associated with bleeding, especially intracranial bleeding. The risks of aspirin late in pregnancy are probably not relevant for a topical exposure to salicylic acid, even late in the pregnancy, because of its low systemic levels. Topical salicylic acid is common in many over-the-counter dermatological agents, and the lack of adverse reports suggests a low teratogenic potential.
Salicylic acid overdose can lead to salicylate intoxication, which often presents clinically in a state of metabolic acidosis with compensatory respiratory alkalosis. In patients presenting with an acute overdose, a 16% morbidity rate and a 1% mortality rate are observed.
Some people are hypersensitive to salicylic acid and related compounds.
The United States Food and Drug Administration recommends the use of sun protection when using skincare products containing salicylic acid (or any other BHA) on sun-exposed skin areas.
There is data that supports an association between exposure to salicylic acid and Reye's Syndrome. The National Reye's Syndrome Foundation cautions against the usage of these substances, and other substances similar to aspirin, on children and adolescents.
Epidemiological research has shown an association between the development of Reye's Syndrome and the use of aspirin (a salicylate compound) for treating the symptoms of influenza-like illnesses, chicken pox, colds, etc.
The U.S. Surgeon General, the Food and Drug Administration, the Centers for Disease Control and Prevention, and the American Academy of Pediatrics recommend that aspirin and combination products containing aspirin not be given to children under 19 years of age during episodes of fever-causing illnesses, because of a concern about Reye's Syndrome.
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