9 min read
Chemical Exfoliation Explained: AHA vs BHA vs PHA
This page contains affiliate links. As an Amazon Associate I earn from qualifying purchases.
Key takeaways
- AHAs such as glycolic and lactic acid are water-soluble and work on surface texture and tone.
- Salicylic acid is a BHA and is oil-soluble, which lets it clear inside the pore on oily and acne-prone skin.
- PHAs such as gluconolactone have larger molecules, penetrate less, and suit sensitive skin.
- One exfoliating product, used one to three times a week, is enough for almost every skin type.
Chemical exfoliants dissolve the bonds holding dead cells to the surface of your skin, rather than scraping them off. Done correctly, that means smoother texture, clearer pores, better product absorption, and faster fading of marks. Done badly — too strong, too often, stacked with a retinoid — it means a stripped barrier that takes months to rebuild. The difference is almost entirely in choosing the right acid family and the right frequency.
Written by Maria Alejandra, founder and editor · Last updated:
Independently researched and reviewed for accuracy. Read our editorial policy or how we research routines.
More cards from this guide
AHAs: surface texture and tone
Alpha hydroxy acids are water-soluble, so they work on the skin's surface. They are the right choice for dryness, dullness, uneven tone, fine lines, and rough texture — not for congestion deep in the pore.
- Glycolic acid — the smallest molecule, deepest penetration, strongest results and strongest sting. Best for normal to oily, resilient, non-sensitive skin. 5–10% for home use.
- Lactic acid — larger molecule, gentler, and humectant, so it hydrates while it exfoliates. The best AHA for dry skin. 5–10%.
- Mandelic acid — largest molecule, slowest and gentlest penetration, with mild antibacterial action. The safest AHA for sensitive skin and for deeper skin tones, where aggressive exfoliation risks post-inflammatory hyperpigmentation. 5–10%.
BHA: inside the pore
Salicylic acid is oil-soluble, which is the entire point — it can travel through sebum into the follicle and clear it from the inside. That makes it the correct choice for blackheads, closed comedones, oily skin, and mild inflammatory acne. It is also anti-inflammatory, related structurally to aspirin, so it calms as well as clears.
Effective home strengths are 0.5% to 2%. Two percent leave-on liquids are the classic format; 0.5% to 2% cleansers give a lower-contact option for sensitive or dry skin that still gets congested. It is not the right pick for dry skin with no congestion — you will get flaking without benefit.
PHA: the gentle option that still works
Polyhydroxy acids — gluconolactone and lactobionic acid — are chemically similar to AHAs but with much larger molecules and additional hydroxyl groups. They exfoliate more slowly and superficially, hold water at the surface, and have antioxidant properties.
They are the reasonable choice for rosacea-prone, eczema-prone, very sensitive, or freshly retinized skin, and for anyone who wants to exfoliate more frequently without cumulative irritation. Expect subtler results over a longer period; that trade is the point.
Matching acid to skin type
Match the acid family to the problem you actually have:
- Oily, congested, blackheads — salicylic acid 2%, two to three times a week.
- Dry, flaky, dull — lactic acid 5–10%, one to two times a week.
- Combination — salicylic in the T-zone, lactic on the cheeks, or alternate nights.
- Sensitive or rosacea-prone — PHA, up to three times a week, or mandelic acid once weekly.
- Deeper skin tones with dark marks — mandelic or PHA first; aggressive glycolic peels can worsen pigmentation.
- Mature skin with fine lines — glycolic 5–8% if tolerated, otherwise lactic.
How often, and how to build up
Start once a week, on clean dry skin, at night, followed by moisturizer. Hold that frequency for about two weeks. If there is no tightness, stinging, or flaking, move to twice a week. Most routines settle somewhere between one and three times a week — that is where we suggest landing rather than a physiological limit, and it moves with the acid, its strength and your barrier. Your product's own label instructions come first. Once a week is a perfectly effective long-term routine.
Our advice is to keep an exfoliant and a retinoid on separate nights, and to avoid two leave-on exfoliants in one night. That is an irritation-avoidance strategy rather than a chemical incompatibility: skin that has used both comfortably for a long time, or a routine a clinician has set up, can look different. Skip exfoliation in the 48 hours before or after waxing, threading, laser, or shaving irritated skin.
Signs you are over-exfoliating
Stop immediately if you notice any of these:
- A tight, shiny, waxy look rather than a smooth one.
- Stinging from products that used to feel neutral, including plain moisturizer.
- Increased redness, or small bumpy dermatitis around the mouth and nose.
- A greasy-feeling film over skin that still feels tight underneath.
- New breakouts in unusual places, or marks that fade more slowly than before.
The non-negotiable: sunscreen
AHA products carry a sun-sensitivity warning for a reason: measured photosensitivity rises with use and stays raised for a period after stopping, which is why the labeling requires it. Using AHAs without daily broad-spectrum SPF 30+ works against the pigment you are treating, and in our experience it is one of the most common reasons people conclude that acids 'did nothing' for their dark marks.
If you are not willing to wear sunscreen every day, use a BHA cleanser or a PHA instead of a leave-on AHA, and rely on retinoids and niacinamide for tone.
Frequently asked
- What is the difference between AHA and BHA?
- AHAs are water-soluble and work on the skin's surface for tone and texture. BHA (salicylic acid) is oil-soluble and penetrates into the pore, so it suits congestion and acne.
- Which acid is best for sensitive skin?
- PHAs such as gluconolactone, or mandelic acid. Both use large molecules that penetrate slowly, so they exfoliate with much less irritation.
- How often should you chemically exfoliate?
- Start once a week and build towards two or three times a week if your skin stays comfortable. That upper end is our tolerability advice rather than a fixed limit — the acid, its strength and your barrier all move it, and more frequent use is where most people run into barrier trouble.
- Can I use an acid and retinol on the same night?
- Not until both are well tolerated separately over several months. Alternating nights is safer and just as effective.
