Acids in skincare: how to start without burning your skin

Your cart looks like a mini lab: a glycolic acid toner, a BHA serum, a PHA peel — each one from a different video. Right before you hit "buy," one thought creeps in: what if I hurt my skin?

One clip of a red, flaking face is enough to close the app and reach for plain moisturizer instead. The truth is simpler than the fear suggests: acids don't burn skin on their own. They burn when you dose them wrong — too strong, too often, too fast, all at once. Everything else is a protocol you can write down step by step.

AHA, BHA, PHA: what's the difference

AHAs — glycolic, lactic, mandelic acid — are water-soluble and exfoliate by loosening the bonds between cells in the skin's outer layer (Almeman, Clinical, Cosmetic and Investigational Dermatology 2024). Molecule size decides how deep an acid reaches and how much it can irritate. Glycolic acid has the smallest molecule among the popular AHAs, so it penetrates fastest and deepest — hence its strength, and its higher irritation risk. Lactic acid works more slowly and hydrates on top of that. Mandelic acid, with the largest molecule, is the gentlest of the three, which is why it's recommended for sensitive skin and deeper skin tones, where the risk of post-inflammatory hyperpigmentation runs higher. In one study, 45% mandelic acid performed similarly to 30% salicylic acid in acne peels, with a different tolerability profile (Dayal et al., Journal of Cosmetic Dermatology 2020). Those are professional-strength concentrations, though, not at-home ones.

BHA — salicylic acid — is oil-soluble. That lets it travel into sebum-rich environments: the hair follicle and the pore itself. There, it loosens the structures holding dead skin cells together instead of dissolving them outright (Lévêque et al., Skin Research and Technology 1995). That's why BHA works well on oily skin and enlarged pores — it reaches where AHA can't.

PHAs — gluconolactone, lactobionic acid — exfoliate through a mechanism similar to AHAs, but their larger molecule penetrates slower and gentler. They also hydrate and support the skin barrier. In one study of 16 women, a peel was applied to one half of the face; gluconolactone at 10% and 30% changed skin pH, water loss, and sebum levels (Jarząbek-Perz et al., Journal of Cosmetic Dermatology 2023). That's why PHA is now the go-to starter acid for skin with no exfoliation history.

The starter protocol, step by step

Before anything touches your face, patch-test on your forearm. Apply the product to the inner arm and watch the skin for 24 to 48 hours. Allergic reactions can be delayed, showing up only after many hours. If nothing happens, move the test to your face, but keep it local — the jawline first, not the whole cheek.

For the first three weeks, use the acid once a week and watch how your skin responds. Only then increase — frequency or concentration, never both at once. Wait at least a week after each change before making the next one. The American Academy of Dermatology's rule is simple: the stronger an acid exfoliates, the less often it belongs on your skin.

A brief, mild tingle on application is usually just the low pH at work, not a warning sign. What should make you stop is different: stinging pain, redness that lasts more than a day, a tight feeling, flaking, a shiny "polished" look to the skin, or a sting when you apply plain moisturizer afterward. Those are signs the skin barrier is compromised — the response is to cut back, not push through.

The mistakes that irritate skin most

Using an acid and retinol on the same night is the most common beginner mistake. The claim that one "neutralizes" or "deactivates" the other has no backing in the research — it's a recycled industry myth, not a chemical fact. The real risk is different: two active exfoliants at once put a heavier load on the skin and worsen dryness and irritation, especially early on. Vitamin C in its pure L-ascorbic acid form works at a low pH, which makes it harder to combine with retinol in a single application too. The simpler fix: acids in the morning, or on a different night than retinol — alternating nights works as well.

SPF is non-negotiable alongside acids. The FDA requires AHA cosmetics to carry a warning label: "Sunburn Alert: this product contains an alpha hydroxy acid (AHA) that may increase your skin's sensitivity to the sun" (FDA, Guidance for Industry: Labeling for Cosmetics Containing Alpha Hydroxy Acids). That heightened sensitivity lasts for the entire time you use the acid, plus roughly a week after you stop.

The third mistake is mixing chemical and physical exfoliation — an acid and a scrub on the same day. That's a double load on the skin barrier, and it tends to end in inflammation and dehydration. If you want both methods, split them across the week: one scrub, two or three acid sessions, always on different days.

How far you can go at home, and when to see a specialist

Over-the-counter products have a concentration ceiling for a reason. The US FDA caps AHA in at-home cosmetics at 10%, at a pH of 3.5 or higher (Almeman 2024). For salicylic acid (BHA) in over-the-counter acne products, that limit is 0.5–2%.

In a professional setting, those numbers look different. A trained specialist can use glycolic acid up to 30% at around pH 3.0 for a superficial peel. Deeper peels go up to 20–70%, always with thorough rinsing and SPF protection afterward (Almeman 2024). What makes the difference is knowing how to neutralize the acid and matching the concentration to your skin's phototype. Get that match wrong, and the risk of post-inflammatory hyperpigmentation climbs, especially on deeper skin tones.

When is it worth moving from a home routine to a specialist's care? When a few weeks at a low concentration bring zero visible change. Or the opposite: your skin reacts harder than it should — persistent redness, new dark spots, acne scarring. That's a cue to book a specialist, not to raise the concentration yourself.

Which acid to start with

Sensitive, dry skin with a compromised barrier — start with PHA or lactic acid. The larger molecule penetrates more slowly, and the added hydration and barrier support lower the risk of irritation.

Oily skin, enlarged pores, prone to breakouts — this is BHA territory. A 2% salicylic acid leave-on is one of the most commonly recommended picks — the Paula's Choice SKIN PERFECTING 2% BHA Liquid Exfoliant, for instance.

Skin that tolerates actives well and wants a more even tone and texture — that's where AHA shines: lactic acid for a gentler start, glycolic acid once you're more experienced.

Start with one acid, not three at once. Learn how your skin reacts before you build a full routine around it — it's a simpler, safer start than experimenting on multiple fronts at the same time.