Skin Care Education

BHA (Beta Hydroxy Acids)

A family of oil-soluble chemical exfoliants that penetrate into the pore lining to dissolve congestion, reduce breakouts, and refine skin texture from within the follicle as well as at the surface.

What Are Beta Hydroxy Acids?

Beta hydroxy acids, commonly abbreviated to BHAs, are a category of chemical exfoliants distinguished from alpha hydroxy acids primarily by their solubility. Where AHAs are water-soluble and work at the skin surface, BHAs are oil-soluble, meaning they can dissolve in sebum and travel down into the pore lining alongside the skin’s natural oil. This gives them a unique ability to exfoliate from within the follicle as well as at the surface, making them particularly effective for treating congestion, blackheads, whiteheads, and acne-prone skin.

Salicylic acid is by far the most widely used BHA in aesthetic practice. It is derived from willow bark and has been used medicinally for centuries. In skincare, it is used at concentrations ranging from approximately 0.5 to 2 percent in leave-on products and up to 30 percent in professional chemical peel formulations. Salicylic acid has both exfoliating and anti-inflammatory properties, which is why it is effective not only for clearing congestion but also for reducing the redness and inflammation associated with active acne lesions.

Other beta hydroxy acids include beta-hydroxybutanoic acid and tropic acid, though these are rarely encountered in mainstream aesthetic practice. Salicylic acid remains the dominant and most clinically studied BHA. It is also related to aspirin chemically, which contributes to its anti-inflammatory mechanism and means that individuals with a known aspirin sensitivity should use it with caution.

What to Expect

BHA products and treatments are generally well tolerated, particularly compared to higher-strength exfoliating treatments. In leave-on skincare at typical concentrations of 1 to 2 percent, most people experience little to no sensation beyond mild tingling on initial application, which tends to diminish as the skin acclimatises.

Professional BHA peels, typically using higher concentrations of salicylic acid, produce a more pronounced exfoliating response. During a professional salicylic acid peel, a tingling or mild stinging sensation is normal. A distinctive feature of salicylic acid peels is that the acid self-neutralises as it dries on the skin, which means it does not require active neutralisation in the way that glycolic acid peels do. A white frosting may be visible on the skin surface during the peel, which is a normal characteristic of salicylic acid at higher concentrations.

Following a professional BHA peel, some redness and light flaking over the following days is expected and reflects the exfoliating process. Most professional BHA peels involve minimal downtime compared to deeper resurfacing treatments. With regular use at appropriate concentrations, BHAs progressively clear congestion, reduce breakout frequency, and refine pore appearance over several weeks to months.

Who It’s For and Results

BHAs are most suited to oily and acne-prone skin types, those with persistent congestion and blackheads, and those with a tendency toward enlarged pores. The oil-solubility of BHAs makes them uniquely capable of penetrating the pore environment, which is why they outperform water-soluble exfoliants in these specific concerns.

They are also well suited to those with combination skin who experience congestion primarily in the T-zone, and to those with a tendency toward mild inflammatory acne who want to reduce breakout frequency and severity without more aggressive prescription treatments. Their anti-inflammatory properties make them more tolerable for acne-prone skin than some other exfoliating acids, which can exacerbate redness and inflammation if the barrier is already compromised.

BHAs are generally less well suited to very dry or sensitive skin as a primary exfoliant, as their ability to dissolve the lipid components of the skin barrier can worsen dryness in already oil-deficient skin. For these skin types, gentler AHAs such as lactic or mandelic acid are often a better fit. Results with BHAs are most reliable with consistent use: improvements in congestion, pore size, and breakout frequency build over several weeks and are maintained with ongoing use.

Frequently Asked Questions: Beta Hydroxy Acids

The primary difference is solubility and therefore where they work. AHAs are water-soluble and act at the skin surface, making them effective for improving overall texture, brightness, and tone. BHAs are oil-soluble and can penetrate into the pore lining alongside sebum, making them effective for clearing congestion, blackheads, and acne. AHAs are generally better suited to dry, sun-damaged, or pigmentation-focused concerns. BHAs are generally better suited to oily, congested, or acne-prone skin. The two can be used in combination in an appropriately designed routine, addressing both surface and pore-level concerns simultaneously.

BHAs can be used on sensitive skin with care, but they are not always the first-choice exfoliant for this skin type. Salicylic acid has anti-inflammatory properties that can be helpful for reactive skin prone to redness, but its ability to dissolve lipids means it can compromise the skin barrier in very dry or sensitive skin if overused or used at too high a concentration. For sensitive skin with oily or congested tendencies, a low-concentration BHA used infrequently is often well tolerated. For predominantly dry or sensitised skin without significant congestion, a gentle AHA such as lactic acid is usually more appropriate.

For leave-on BHA products at typical concentrations of 1 to 2 percent, use two to three times per week is a common starting point, building to daily use if the skin tolerates it well. Daily BHA use is appropriate for many oily and acne-prone skin types. Professional BHA peels are typically performed in a course of four to six sessions spaced two to four weeks apart. As with all exfoliating actives, beginning with less frequent use and building gradually based on skin response is the most reliable approach to avoiding over-exfoliation and barrier disruption.

This is an area where guidance varies. Salicylic acid at high concentrations, such as those used in professional peels and some prescription formulations, is generally avoided during pregnancy due to its relationship to aspirin and theoretical systemic absorption concerns. At the lower concentrations found in standard leave-on skincare products, the risk is considered very low, but many healthcare providers recommend caution or avoidance as a precaution. Individuals who are pregnant or planning to become pregnant should discuss their skincare routine with their healthcare provider to determine what is appropriate for their specific circumstances.