Glycolic acid is the strongest of the everyday acids and the one most likely to be oversold to you. It is genuinely useful on body skin in a narrower set of situations than the marketing suggests.
What makes it stronger than lactic acid?
Size. Glycolic acid has the smallest molecule of the alpha hydroxy acids, which means it gets through the surface faster and further than lactic acid at the same concentration.
Everything follows from that. It resurfaces more effectively. It also reaches living tissue sooner, which is why it stings more, why it sensitises skin to sun more, and why a strength that was fine on your back is a mistake on the inside of your arm.
A rough equivalence worth knowing: on body skin, 5% glycolic does approximately what 10–12% lactic does. If you are already getting results from lactic acid, switching buys you irritation and nothing else.
When is glycolic acid the right choice?
Thickened, stubborn patches that lactic acid has not shifted in eight weeks. This is the honest use case — you tried the gentler thing, it did not work.
Rough skin on thick areas — backs, shoulders, the outside of an upper arm. Thick skin tolerates the penetration better than thin skin does.
Dull, uneven surface texture where the goal is resurfacing rather than hydration.
Where it is not the right choice: general dryness, sensitive skin, anywhere already irritated, and — importantly — discolouration on deeper skin tones.
The pigmentation trap
This is the part that gets left out. Glycolic acid is often recommended for the dark marks left behind by body acne. On deeper skin tones it can cause exactly what you are treating, because post-inflammatory hyperpigmentation is triggered by inflammation, and glycolic acid at an aggressive strength is inflammatory.
If dark marks are the problem and your skin tone is deeper, azelaic acid is the better-evidenced and far better-behaved option. That recommendation costs us nothing and saves some readers months.
What an in-clinic peel does that a bottle cannot
Products at home run at 5–10%. Professional peels run at 30–70%. The gap is not just concentration, and it is worth knowing before you buy a high-strength bottle online to close it yourself.
A professional peel is applied for a timed window and then deliberately neutralised. Someone is watching the skin change colour and stopping the process at a defined point. The acid is also at a controlled pH, which affects how aggressively it works as much as the percentage does.
A leave-on product at home does none of that. It is formulated to self-buffer as it works, which is why it does not need neutralising and why it cannot safely be made much stronger. Buying a 30% bottle and applying it like a lotion is not a cheaper version of a peel — it is an unsupervised chemical burn with no stopping mechanism.
If you want the effect of a peel, that is a clinic appointment. If you want gradual resurfacing at home, 7–10% nightly does get there, over months.
Building up without wrecking your skin
The single most useful rule: two weeks of alternate nights before daily use, on one area at a time.
- Week 1–2: alternate nights, one area, on damp skin.
- Week 3: nightly if there has been no lasting redness.
- Any lasting redness or peeling: back to alternate nights for two weeks. Not a lower strength, not a different brand — just less often.
Do not start it on several areas at once. If your shoulders react and your shins do not, that is useful information you can only get by introducing it in one place.
And if the goal is treating dark marks rather than texture, stop here and read azelaic acid first. On deeper skin tones, glycolic acid is a genuine risk of making pigmentation worse, and there is a better-behaved option that does that specific job properly.
What to skip and why
Skip going straight to daily use. Two weeks of alternate nights first. The people who get chemical burns from at-home acids are almost always the ones who skipped the build-up.
Skip it on the day you shave or wax. More true here than for any other acid on this site.
Skip layering it with salicylic acid or a retinoid on the same patch. Pick one active per area and give it eight weeks to answer the question.
| Strength | How often | Time to result |
|---|---|---|
| Strength5% lotion | How oftenNightly | Time to resultComparable to 10–12% lactic · 4 weeks |
| Strength7–10% lotion | How oftenAlternate nights, building to nightly | Time to resultThickened patches soften in 3–4 weeks |
| StrengthBuild-up period | How often2 weeks minimum before daily use | Time to resultSkipping this is the main cause of irritation |
| StrengthSun sensitivity | How oftenSPF on exposed skin, for a week after stopping | Time to resultHigher than with lactic acid |
On body skin, glycolic acid at 5% does roughly what lactic acid does at 10–12%. If lactic acid already works for you, there is no benefit in switching.
What the strengths on a label mean
- 5%
- Body lotions sold as resurfacing. Mild, tolerable nightly, and roughly equivalent in effect to a 10% lactic acid.
- 7–10%
- The useful home range for thickened or discoloured body skin. Start on alternate nights; most people never need to go higher.
- 15–20%
- Aggressive at-home strength. Real resurfacing, real risk of a chemical burn on skin that was not built up to it slowly.
- 30–70% (in-clinic)
- A professional peel, timed and neutralised by someone trained. The difference between this and a bottle is supervision, not just percentage.
Leave it alone if: you have deeper skin tone and are treating discolouration — glycolic acid can trigger post-inflammatory hyperpigmentation, which is the exact thing you were trying to fix. Azelaic acid is the safer route.
What it is used for on this site
Questions people ask
- Is glycolic acid better than lactic acid?
- Stronger, not better. It has the smallest molecule of the alpha hydroxy acids, so it penetrates further and works faster — and irritates faster for the same reason. On thickened or discoloured patches that is a good trade. On ordinary dry, rough body skin, lactic acid gets you to the same place with less collateral damage.
- Can glycolic acid help with dark marks left by body acne?
- Sometimes, by speeding up turnover of the pigmented surface cells. But if your skin tone is deeper, glycolic acid carries a real risk of causing more pigmentation than it clears, because the irritation itself triggers it. Azelaic acid is the better-behaved option for that specific job.
- Why does glycolic acid sting more than the other acids?
- Small molecule, fast penetration, low pH. It reaches living tissue sooner than lactic acid does. A brief tingle is normal; burning, lasting redness or peeling means the strength or frequency is wrong for your skin, not that it is working harder.
- Can I use it on my back and shoulders for bumpy skin?
- Yes, and the back tolerates it better than most areas because the skin is thick. Applying it yourself is the practical problem — a lotion on a long-handled applicator, or a pad, beats contorting. Skip the days you shave or wax anything in the area.
- Do I need to neutralise it like a salon peel?
- Not with a leave-on product at home strengths — those are formulated to be left on and to self-buffer as they work. Neutralising applies to professional peels at 30% and above, where the acid is deliberately left on for a timed window and then stopped.
What this page is based on
4 named sources, linked in full. No "studies show".
- Cleveland Clinic
- Cleveland Clinic
- Cleveland Clinic
- American Academy of Dermatology