How to Start Using Acids in Skincare (Without Ruining Your Skin)

The Biochemistry of Exfoliation: What Acids Actually Do

Understanding how chemical exfoliants work at the molecular level explains both why they are effective and why over-use is so common — because the mechanism that makes them powerful also makes it easy to disrupt more than intended.

The stratum corneum is composed of corneocytes — flattened, protein-filled dead skin cells — held together by corneodesmosomes, protein structures that act as molecular rivets between cells. Normal desquamation (skin shedding) occurs when enzymes called serine proteases break down these corneodesmosomes, allowing dead cells to shed individually and invisibly. AHAs and BHAs accelerate this process by a different mechanism: they reduce the pH of the stratum corneum, which both activates the serine proteases directly and weakens the ionic bonds that maintain corneodesmosomes. The result is faster, more synchronised shedding of the surface dead cell layer.

This is why chemical exfoliation works so much better than physical scrubs: instead of physically tearing cells off the surface (which disrupts the barrier randomly and can cause micro-tears), acids dissolve the specific molecular connections holding dead cells together, allowing them to shed cleanly while leaving the living skin layers below undisturbed. It is precise rather than mechanical.

The risk of over-use flows from the same mechanism. If acids are applied so frequently that the stratum corneum does not have time to reconstitute its normal density before the next application, the protective dead-cell layer becomes chronically thin — leaving the living layers of the epidermis more exposed, the barrier more permeable, and the skin more reactive to everything from weather to other skincare ingredients.

Reading Your Skin's Response: What's Normal vs What's a Problem

The ability to distinguish normal adaptation responses from genuine over-exfoliation or allergic reactions is one of the most practically useful skills for anyone starting acids. Getting this distinction wrong in either direction — abandoning an acid that is working normally, or persisting with one that is causing damage — leads to worse outcomes than getting it right.

Normal responses in the first two to four weeks: Mild tingling on application, particularly with glycolic acid and AHAs at lower pH. Some flaking or light peeling as the accumulated dead cell layer begins to shed more rapidly — this is the exfoliant doing its job. Slightly increased sensitivity to other products in the first few days after application, resolving by the following day. A temporary slightly shinier appearance as fresher, more hydrated skin cells are revealed. All of these are expected and do not indicate a problem.

Responses that signal a problem: Burning that persists beyond five to ten minutes of application, or that is significantly more intense than the initial mild tingling. Redness that does not resolve within twenty-four hours. Breakouts in areas where you do not normally experience them (purging in existing acne-prone areas is normal; new-location breakouts suggest a reaction). Skin that feels raw, tight, or unusually shiny and sensitive for multiple days after a single application. Stinging in response to products that previously caused no reaction — including water. These indicate the acid is disrupting the barrier faster than it can repair, and the frequency or concentration needs to be reduced immediately.

Building From Beginner to Advanced: A Progression Framework

Chemical exfoliation is not a static practice — the right approach at six weeks of acid use is different from the right approach at six months, and different again at two years of consistent use. Understanding the progression prevents stagnation at a level that is working below your skin's current tolerance capacity, and prevents over-reaching into territory where the skin is not yet ready.

Phase 1 — Introduction (weeks 1–8): Once per week application of a beginner-appropriate acid (lactic 5%, PHA, or salicylic 0.5%) to clean, dry skin. Goal: establish tolerance and identify any sensitivities before increasing. Success indicator: no persistent redness, no barrier symptoms, some improvement in skin texture and brightness.

Phase 2 — Building frequency (months 2–4): Increase to twice weekly if phase 1 was entirely comfortable. If using a single acid type, maintain the same product but increase frequency. Begin to differentiate between AHA nights (texture, brightness, anti-ageing) and BHA nights (pore clarity, oiliness) if using both — alternating rather than combining. Success indicator: consistent exfoliation benefit without irritation on the non-exfoliation nights.

Phase 3 — Optimised routine (months 4+): Two to three times weekly for most skin types. Adjust acid type based on emerging skin needs — shifting to glycolic if texture refinement is the priority, increasing salicylic frequency if congestion is persistent. Introduce retinol as an alternating PM active if not already using it. The key at this stage: rest nights are still essential. Two nights per week of ceramide-only repair are not optional even for experienced acid users.

Advanced considerations: At-home peels (glycolic 20–30% for five to ten minutes, used monthly) offer a step up in cell renewal intensity that daily use of lower concentrations cannot match. These should only be introduced after at least three to four months of consistent lower-percentage acid use and should be approached with the same slow-introduction caution as starting acids initially.

Common Questions About Starting Acids

Can you use acids if you have active acne?

Yes — and for oily, congested, acne-prone skin, BHAs are one of the most effective interventions available. Salicylic acid at 0.5–2% penetrates the pore lining and dissolves the sebum plug that precedes blackheads and inflammatory acne. The anti-inflammatory properties of salicylic acid (related to its aspirin chemistry) additionally reduce the redness and swelling of active breakouts. AHAs are less directly targeted at acne but provide complementary benefits for post-acne marks and texture. The concern with acids and active acne is not whether to use them but how — avoiding over-exfoliation, which damages the already-compromised barrier of acne-prone skin and worsens inflammation.

Do acids make skin thinner over time?

No — this is a persistent myth based on misunderstanding what exfoliation does. AHAs and BHAs remove accumulated dead cells from the stratum corneum surface, but they do not thin the living epidermis beneath. In fact, consistent retinol use (often used alongside acids) demonstrably increases epidermal thickness over time by stimulating cell production. The sensation of "thinner-feeling" skin after starting acids is the removal of the dead-cell buildup that was adding apparent thickness without any functional benefit — the underlying skin architecture is unchanged or improved.

Can you use acids during pregnancy?

Low-percentage lactic acid and glycolic acid (5–10%) are generally considered safe during pregnancy at typical cosmetic use levels. BHAs (salicylic acid) are generally advised against during pregnancy at high doses — while the risk from topical cosmetic use is considered low, many practitioners recommend avoiding BHAs as a precaution given the systemic salicylate exposure concern from oral aspirin in pregnancy. PHAs have no identified safety concerns in pregnancy. As with all skincare during pregnancy, consulting with a healthcare provider for specific guidance is the appropriate approach.