Chemical exfoliants: what AHAs and BHAs actually do.

Chemical exfoliants have become a fixture in modern skincare routines. Alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs) are among the most sold categories of skincare actives. They are also among the most frequently overused. Understanding what they do — and what that means for the barrier — makes it easier to use them well.

What they are

AHAs — alpha hydroxy acids. Water-soluble acids derived from natural sources. Glycolic acid (derived from cane sugar) has the smallest molecular size and penetrates most readily; lactic acid (from milk) is gentler and also functions as a humectant; mandelic acid (from almonds) is gentler still, with a larger molecular size that limits penetration. All AHAs work primarily at the skin surface.

BHAs — beta hydroxy acids. The primary BHA used in skincare is salicylic acid, derived from willow bark. Salicylic acid is oil-soluble, which allows it to penetrate into the oil-filled pore lining — a property AHAs lack. This makes it specifically useful for acne-prone and oily skin types.

What they do

AHAs and BHAs both work by loosening the bonds — called desmosomes — that hold dead skin cells together at the surface. By weakening those bonds, they allow the outermost layer of dead cells to shed more readily, revealing the newer cells beneath.

The effects of this are real and well-documented:

• Improved texture — the surface is smoother when fewer dead cells are accumulating on it
• More even tone — pigmented cells dispersed more rapidly reduce visible unevenness
• Reduced comedones — BHAs, by clearing the pore lining, prevent the dead-cell build-up that causes blackheads and non-inflamed breakouts
• Improved penetration of subsequent products into a thinner dead-cell layer

These are genuine effects, not marketing claims.

The overuse problem

The most common issue with chemical exfoliants is using them too frequently.

The stratum corneum — the outermost barrier layer — is made up of the dead cells that exfoliants remove. It is not waste; it is the barrier. Its job is to prevent water from leaving and irritants from entering. When exfoliants are used too aggressively or too often, they remove barrier layers faster than the skin can rebuild them.

The result is thin, compromised, reactive skin: tight after washing, red, sensitised to ingredients that would not normally cause reactions, and prone to further irritation from the same exfoliant that seemed fine initially. This is sometimes called over-exfoliation, and it is an extremely common outcome of following advice that positions daily exfoliation as the path to glowing skin.

Daily exfoliation is not appropriate for most people. Twice-daily exfoliation causes barrier damage in almost everyone.

How to use them well

Once or twice a week. For most people, that is enough to see the benefits without compromising the barrier. Some people find that once every one to two weeks is sufficient. Start infrequently and observe how the skin responds.

Not on compromised skin. If the barrier is already disrupted — dry, reactive, sensitised, or recovering from another active — exfoliation adds to the disruption. The baseline must be stable first.

Not layered with retinol on the same night. Both accelerate cell turnover. Using them simultaneously is not an amplification of the benefit; it is a multiplication of the irritation.

Low concentrations first. A leave-on AHA at 5–7% glycolic acid is a reasonable starting point. Products with AHA concentrations of 15–30% are intended for occasional treatment or professional use, not daily applications.

AHAs and SPF. AHAs increase photosensitivity — the fresher surface is more susceptible to UV damage. Evening application and consistent daily sunscreen matter more when exfoliants are part of a routine.

Where they fit

Chemical exfoliants are effective tools for specific concerns: persistent texture, congestion, dullness, or post-inflammatory marks that a simple routine has not resolved. They are not a baseline requirement.

The Lux & Glo ritual does not include a chemical exfoliant. The oil cleanser removes surface residue without disrupting pH. Niacinamide strengthens the barrier from within, and squalane reinforces the lipid matrix. For skin that is reactive, compromised, or new to skincare, building the barrier comes before adding ingredients designed to accelerate its turnover.

Exfoliants work better — and cause fewer problems — on a stable, intact baseline.