Salicylic acid: A fat-soluble exfoliant for clearing pores and acne

What it is

Salicylic acid (a beta hydroxy acid, BHA) is fat-soluble: it penetrates sebum and exfoliates inside the pore. Unlike the alpha hydroxy acids (glycolic, lactic), which are water-soluble and work on the surface, BHA dissolves sebum and helps clear blackheads and whiteheads.

It is very useful in mild acne, clogged pores and oily skin, and it usually irritates less than AHAs. In cosmetics it is used at 0.5–2%. It causes less photosensitivity than AHAs, although sunscreen is part of any routine with exfoliants.

Mechanism of action

It works through:

Fat solubility: it penetrates sebum, dissolving comedones
Keratolytic exfoliation in the hair follicles
Anti-inflammatory: it reduces follicular inflammation

At the counter

When to recommend it

Mild to moderate acne (comedones / papules)
Enlarged, clogged pores
Oily skin prone to comedones
Gentle exfoliation (compared with the more irritating AHAs)

When not to

Allergy to salicylates
Very irritated / inflamed skin (wait until it settles)
Severe / cystic acne (needs dermatological treatment)
Pregnancy: at low concentration and on small areas it is usually accepted; avoid peels and large areas

What to say at the counter. To start: a low concentration, 2–3 nights a week, increasing if tolerated. Sunscreen during the day. And do not start it on the same day as an AHA or a retinoid: one at a time.

Warnings

Important Absorption: in young children or over large areas, enough can be absorbed to cause salicylate toxicity. Do not use on infants or over large areas.
Caution Irritation: itching or redness is normal at first. Reduce the frequency if it is severe.
Caution Photosensitivity: less than with AHAs, but sunscreen is still part of the routine.
Caution Incompatibility: do NOT combine with an AHA at the same time (too much exfoliation).

Pharmacokinetics

Absorption: Rapid skin absorption. Its fat solubility allows deep follicular penetration.
Distribution: Mainly local action in the epidermis and follicles.
Metabolism: Local keratolytic action.
Elimination: Shed with skin turnover; minimal systemic absorption.

Salicylic acid (BHA) vs glycolic acid (AHA)

Aspect	Salicylic acid (BHA)	Glycolic acid (AHA)
Fat solubility	Yes (penetrates sebum)	No (water-soluble)
Effect on acne / comedones	Excellent (dissolves sebum)	Moderate
Irritation	Moderate	Moderate to high
Sensitive skin	Better tolerated	More irritation
Ideal indication	Acne, pores, oily skin	General renewal, scars

BHA for acne and comedones. AHA for photo-ageing and scars.

Self-assessment

Three questions. When you check your answers you will see the explanation for each one.

What is the main advantage of BHA over AHA? It causes no irritation It is more potent Fat solubility: it penetrates sebum to dissolve comedones. Better for acne
Can BHA and AHA be combined at the same time? Yes, they boost each other It depends on the concentration No, too much exfoliation. Space them out or alternate (different nights)
What is the protocol for starting BHA on sensitive skin? Every 2 weeks A low concentration (0.5%) 2–3 times a week, increasing gradually if tolerated Daily, at a high concentration

Training content. It does not replace the summary of product characteristics or clinical judgement.

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