Salicylic Acid, Glycolic Acid, Lactic Acid: A Plain-English Guide to Chemical Exfoliants
Key Takeaways
- AHAs like glycolic and lactic acid work on the skin's surface and suit most skin types.
- Salicylic acid (a BHA) is oil-soluble, making it uniquely effective inside pores for oily or acne-prone skin.
- PHAs are the mildest chemical exfoliants and are generally well-tolerated by sensitive skin.
- Sun protection is essential whenever you use any chemical exfoliant.
- Start slowly — once or twice a week — and increase frequency only as your skin tolerates it.
What Is Chemical Exfoliation?
Physical exfoliation uses friction — think scrubs or brushes — to buff away dead skin cells. Chemical exfoliation works differently: specific acids dissolve the bonds holding dead cells to the surface, allowing them to shed more evenly and with less abrasion. The result, with consistent use, is typically smoother texture, more even tone, and skin that responds better to the rest of your routine.
The three main categories — AHAs (alpha-hydroxy acids), BHAs (beta-hydroxy acids), and PHAs (polyhydroxy acids) — each work through a slightly different mechanism and suit different concerns. Knowing your skin type is the first step to choosing the right one.
0.5%–2%
Salicylic acid range in OTC products
The U.S. FDA recognizes salicylic acid as a safe and effective acne-fighting active ingredient at concentrations between 0.5% and 2% in over-the-counter formulations.
5%–10%
Typical OTC AHA concentration range
Dermatologists generally consider AHA concentrations between 5% and 10% appropriate for home use, with professional-grade treatments reaching significantly higher levels.
AHAs: Glycolic and Lactic Acid
Alpha-hydroxy acids are water-soluble and work primarily at the skin's surface. Glycolic acid — derived from sugarcane — has the smallest molecular size of the common AHAs, which allows it to penetrate quickly. It's widely studied for improving skin texture, uneven tone, and the appearance of fine lines. Because it acts fast and penetrates readily, it can cause more irritation than other AHAs, particularly at higher concentrations.
Lactic acid — found naturally in milk — has a larger molecule than glycolic acid and penetrates more slowly. This makes it somewhat gentler while still delivering meaningful exfoliation. Lactic acid also has mild humectant (moisture-attracting) properties, which can make it a better fit for people who find glycolic acid drying.
Both are best used in the evening, as AHAs increase photosensitivity. Concentrations in over-the-counter products typically range from 5% to 10%, which is suitable for most home routines. Higher concentrations are used in professional settings.
If you're new to AHAs, start with lactic acid rather than glycolic — it's gentler and gives your skin time to build tolerance before stepping up to a stronger option.
Glycolic acid's small molecule size means faster penetration, which increases the chance of irritation on skin that hasn't been introduced to chemical exfoliation before.
Apply your chemical exfoliant to clean, fully dry skin. Even slight dampness can increase penetration and tip a tolerable product into an irritating one.
Water on the skin temporarily lowers the surface pH, which can intensify the activity of acid-based products beyond the intended level.
BHAs: Salicylic Acid
Salicylic acid is the most commonly used BHA in skincare. Unlike AHAs, it is oil-soluble, which means it can travel through sebum (the skin's natural oil) and work inside the pore lining — not just on the surface. This makes it particularly useful for congested pores, blackheads, and inflammatory acne.
Salicylic acid also has mild anti-inflammatory properties, which can help reduce the redness associated with breakouts. Typical over-the-counter concentrations range from 0.5% to 2%. If you have oily or acne-prone skin, salicylic acid is generally considered the starting point for chemical exfoliation.
Salicylic Acid and Aspirin Sensitivity
Salicylic acid is chemically related to aspirin (acetylsalicylic acid). People with a known aspirin allergy or sensitivity should consult a dermatologist or healthcare professional before using salicylic acid topically. Additionally, salicylic acid is generally not recommended during pregnancy — always seek guidance from a healthcare provider if this applies to you.
PHAs: The Gentler Option
Polyhydroxy acids — including gluconolactone and lactobionic acid — are the largest-molecule group, which means they penetrate the skin the most slowly. This slower action is what makes them the least likely to cause stinging, redness, or irritation.
PHAs offer similar surface-level exfoliation to AHAs, and some research suggests they may also have antioxidant and moisture-retaining properties. They're generally considered a suitable starting point for people with sensitive skin or for anyone new to chemical exfoliation who wants to build tolerance gradually.
Matching Acids to Your Skin Type
No single acid is universally right. The following generalizations can help guide your starting point — though individual responses vary and patch testing is always recommended before committing to regular use.
- Oily or acne-prone: Salicylic acid (BHA) is typically the most targeted choice.
- Dry or dull: Lactic acid (AHA) offers exfoliation with some added hydration benefit.
- Uneven texture or tone on resilient skin: Glycolic acid (AHA) delivers effective surface renewal.
- Sensitive or reactive skin: PHAs are the gentlest entry point.
- Combination skin: Some people use a BHA on oilier areas and an AHA elsewhere, though this requires careful introduction.
For a deeper look at how skin type should shape your entire routine, see our guide on understanding your skin type.
Do Not Mix Exfoliants Without Guidance
Using multiple chemical exfoliants in the same routine — or combining them with retinoids — significantly increases the risk of skin barrier disruption. This can cause persistent redness, peeling, and heightened sensitivity. Unless a qualified dermatologist has specifically recommended a combination approach for your skin, treat one acid at a time and give your skin time to adjust.
How to Use Chemical Exfoliants Safely
The most common mistake with chemical exfoliants is overuse. More frequent application does not accelerate results — it increases the likelihood of a compromised skin barrier, which presents as redness, tightness, or increased sensitivity. Start with once or twice per week and observe how your skin responds over two to four weeks before increasing frequency.
Layering acids with other active ingredients — particularly retinoids or other exfoliants — requires care. Our guide to skincare layering explains how to sequence products to avoid interactions that reduce effectiveness or increase irritation.
Before adding any new exfoliant to your routine, run through a practical checklist for switching products safely — including patch testing on a small skin area first.
Sun protection is non-negotiable. AHAs and BHAs both increase the skin's sensitivity to UV radiation. A broad-spectrum SPF of 30 or higher, applied every morning, is essential. This isn't optional — it's the step that prevents the exfoliant from causing the very unevenness you're trying to address.
Ease In With One Acid at a Time
Resist the urge to combine multiple exfoliating acids when you're starting out. Introduce one product, use it consistently for three to four weeks, and assess your skin's response before considering any addition. This makes it much easier to identify the source of any irritation and keeps your routine manageable.
This article is for general informational and educational purposes only. It is not a substitute for advice from a qualified dermatologist or healthcare professional. If you experience persistent irritation, allergic reactions, or skin concerns, consult a licensed skincare professional.