What is salicylic acid, and is it a BHA?

Salicylic acid is one of the oldest acne ingredients you can buy without a prescription. You will see it on face washes, toners, pads, gels and creams, and often the front of the bottle says "BHA" instead. For what it does once it is on your skin, see the hub guide, what salicylic acid does for your skin.

Salicylic acid in short

Salicylic acid is an acid found in plants such as willow bark, and also made in labs, that is sold both as an acne medicine and as a cosmetic exfoliant. MedlinePlus, the drug information service of the U.S. National Library of Medicine, says topical salicylic acid is used "to help clear and prevent pimples and skin blemishes in people who have acne." In the United States, the FDA's rules for acne products list salicylic acid at 0.5 to 2 percent as an allowed active ingredient. A product in that range, labeled as an acne treatment, is a drug with a Drug Facts label, and it must follow the FDA's required directions and warnings.

What it does to pores and dead skin, and how to use it, are covered in the hub guide, what salicylic acid does for your skin. This page covers what the ingredient is.

Its chemical name

The 2015 review in Clinical, Cosmetic and Investigational Dermatology gives the chemical name: 2-hydroxybenzoic acid. The molecule has an acid group and a hydroxyl group, and both are attached directly to a benzene ring, a closed ring of six carbon atoms. Chemists call compounds built on that ring aromatic compounds.

That structure matters for the name. The review explains that the carbon atoms of aromatic compounds are numbered 1, 2, 3, while the Greek letters alpha, beta and gamma are used for straight chains of carbon atoms. By that rule, "beta" does not describe salicylic acid well. The review says one early paper, by Kligman, described salicylic acid as a beta hydroxy acid, while Yu and Van Scott classed it as a phenolic aromatic acid.

Where salicylic acid comes from

Salicylic acid occurs in plants. The 2015 review lists willow bark, sweet birch and wintergreen leaves as natural sources, and says the ingredient can also be made in a lab. The same review traces its use on skin back more than 2,000 years. In the first century, the Roman writer Pliny used willow bark to treat corns and calluses. Chemists isolated the related compound salicin from willow bark in the late 1820s, and the ability of salicylic acid to soften and loosen the top layer of skin was discovered in the 1860s.

That history explains one label detail. The FDA says a BHA ingredient may be listed as salicylic acid "or related substances, such as salicylate, sodium salicylate, and willow extract." So a product that says "willow bark extract" may contain a salicylate, but the label does not tell you how much. An acne drug product lists salicylic acid and its percentage in the active ingredient line.

Why labels call it a BHA

BHA stands for beta hydroxy acid. AHA stands for alpha hydroxy acid, the group that includes glycolic acid and lactic acid. The FDA says both groups act as exfoliants and that "the BHA most commonly used in cosmetics is salicylic acid."

The name has a problem. A footnote on the same FDA page reads: "From a chemist's perspective, salicylic acid is not a true BHA. However, cosmetic companies often refer to it as a BHA and, consequently, many consumers think of it as one." A 2010 review whose first author is a retired FDA scientist says the same thing in plainer terms: calling salicylic acid a BHA "is incorrect." The review explains that the parts of the salicylic acid molecule sit on a ring shape, and both parts act as acids, while true hydroxy acids behave differently. The 2015 review offers a possible reason the name stuck: salicylic acid may have been labeled a beta hydroxy acid when beta hydroxy acid peels came onto the market, to benefit from the popularity of alpha hydroxy acids.

For shopping, the chemistry matters less than the practical result, and the result is easy to remember. On a skincare shelf, "BHA" almost always means salicylic acid. The review adds one detail that does matter: salicylic acid dissolves in fat and oil, "which makes it useful in subjects with oily skin." Glycolic acid, the best known AHA, dissolves in water instead. The guide salicylic acid vs glycolic acid covers what that difference means for your skin.

How salicylic acid relates to aspirin

Aspirin's chemical name is acetylsalicylic acid. The 2015 review describes aspirin as a pain and fever medicine and says that salicylic acid, "being a salicylate," also calms swelling. So the two are chemical relatives with separate uses: aspirin is swallowed, and salicylic acid acne products go on the skin.

The family link has three practical results that come from MedlinePlus:

• Interactions. MedlinePlus lists aspirin and muscle rubs that contain methyl salicylate as products that may interact with salicylic acid on the skin. Tell your doctor or pharmacist if you take aspirin before you start.
• Children and teenagers with flu or chickenpox. MedlinePlus says they "should not use topical salicylic acid unless they have been told to do so by a doctor," because of the risk of Reye's syndrome, a rare and serious illness that affects the brain and liver.
• Allergy. MedlinePlus says to tell your doctor and pharmacist if you are allergic to salicylic acid before using it.

The FDA's page on BHAs also advises people to avoid using BHA products on infants and children. It gives three more precautions for any BHA product: test it on a small area of skin before a large area, follow the label and do not use it more often than it says, and use sun protection while you use it. If a BHA product causes skin irritation or stinging that does not stop, the FDA says to stop using it and talk to a doctor.

Other uses at other strengths

The same ingredient shows up in products for different problems, and the strength changes with the job. MedlinePlus lists acne, psoriasis, dandruff, corns, calluses and warts on the hands or feet. The FDA's rules set a range for each use:

Product type	Salicylic acid strength allowed by the FDA
Acne products	0.5 to 2 percent
Dandruff, psoriasis and seborrheic dermatitis products	1.8 to 3 percent
Wart removers, liquid	5 to 17 percent
Wart removers, plaster	12 to 40 percent

The wart remover rules require the label to say: "Do not use on moles, birthmarks, warts with hair growing from them, genital warts, or warts on the face or mucous membranes." MedlinePlus gives the same warning. A wart product has many times the salicylic acid of an acne product, so never use one on facial acne. The guide salicylic acid strengths and forms walks through each product type.

Drug or cosmetic: two kinds of product

In the United States, salicylic acid is sold under two sets of rules. As an acne drug, it follows the FDA's acne product rules: 0.5 to 2 percent, a Drug Facts label, and set directions and warnings. As a cosmetic ingredient, it is sold as a BHA. The FDA's page on BHAs says it has been claimed that BHAs reduce the look of fine lines and wrinkles and improve skin texture. A cosmetic makes claims about looks, and an acne drug makes claims about treating acne.

The same FDA page reports a safety review of salicylic acid in cosmetics. In February 2000, the Cosmetic Ingredient Review Expert Panel, which the FDA describes as the cosmetic industry's independent body for reviewing the safety of cosmetic ingredients, reached the tentative conclusion that salicylic acid and related substances are "safe as used when formulated to avoid irritation and when formulated to avoid increased sun sensitivity." The panel added that when sun sensitivity would be expected, the directions should include daily sun protection. That is why a BHA toner or serum may tell you to use sunscreen.

Where it fits among acne treatments

How salicylic acid compares with benzoyl peroxide and adapalene, and which acne it suits, is covered in salicylic acid for acne and salicylic acid vs benzoyl peroxide. In short, the AAD's adult acne page says salicylic acid "works best on whiteheads and blackheads," because it unclogs pores and exfoliates the skin, and it names adapalene, benzoyl peroxide and salicylic acid as clinically proven acne-fighting ingredients. Skinli's photo plan starts with adapalene 0.1 percent and benzoyl peroxide 2.5 percent, and leaves salicylic acid out while you use them.

Deep, painful lumps under the skin are a separate form of acne. The AAD's acne treatment page lists salicylic acid among treatments for whiteheads and pimples. The AAD's adult acne page says anyone with large, painful pimples deep in the skin, or acne that leaves scars, needs a dermatologist.

Reading the label

Three lines on the Drug Facts label tell you most of what you need:

1. Active ingredient. Look for "salicylic acid" and a percentage between 0.5 and 2 for an acne product.
2. Uses. An acne product says it is for the treatment or management of acne. The FDA also allows the claim "penetrates pores to" clear or reduce blackheads, whiteheads or pimples.
3. Warnings. Every acne product must say that "skin irritation and dryness is more likely to occur if you use another topical acne medication at the same time."

Before a new product goes on your whole face, MedlinePlus suggests putting a small amount on one or two small areas for 3 days. The guide how to patch test a new skincare product covers that test step by step.