Key Takeaways
- AHAs are water-soluble acids best suited for dry or sun-damaged skin needing surface renewal.
- BHAs are oil-soluble and penetrate pores, making them particularly effective for oily or acne-prone skin.
- PHAs are gentler, larger-molecule acids that work well for sensitive skin or beginners.
- None of these acids should be layered together without guidance, and all increase sun sensitivity.
- Patch testing and slow introduction reduce the risk of irritation when starting any exfoliant.
Our Verdict
AHAs, BHAs, and PHAs each occupy a distinct niche: AHAs resurface and brighten, BHAs clear congested pores, and PHAs offer a gentler entry point. The right choice depends on your skin type, concerns, and tolerance — and for many people, one well-chosen acid used consistently outperforms rotating through all three.
| Best for | Recommended |
|---|---|
| Dry, dull, or sun-damaged skin | AHAs |
| Oily, acne-prone, or congested skin | BHAs |
| Sensitive skin or first-time exfoliant users | PHAs |
| Aging or rosacea-prone skin needing gentle renewal | PHAs |
Why Chemical Exfoliation Works Differently Than Scrubbing
Physical scrubs slough away dead cells mechanically, which can be effective but also harsh — especially on sensitized skin. Chemical exfoliants work differently: they dissolve the bonds holding dead skin cells together, allowing them to shed more evenly without abrasion. The result is typically smoother texture, more even tone, and clearer pores, depending on which type of acid you use.
The three main categories — AHAs (alpha hydroxy acids), BHAs (beta hydroxy acids), and PHAs (polyhydroxy acids) — share this basic mechanism but differ in molecular size, solubility, and how deeply they penetrate. Those differences matter enormously when matching an exfoliant to a skin type. If you're also thinking about how your skin's needs shift over time, the decade-by-decade skin care overview can help put exfoliation in broader context.
| AHAs | BHAs | PHAs | |
|---|---|---|---|
| Solubility | Water-soluble | Oil-soluble | Water-soluble |
| Where it works | Skin surface | Inside pores | Outermost surface layer |
| Best skin type | Dry, dull, sun-damaged | Oily, acne-prone, congested | Sensitive, reactive, or beginners |
| Common examples | Glycolic acid, lactic acid | Salicylic acid | Gluconolactone, lactobionic acid |
| Irritation potential | Moderate | Low to moderate | Low |
| Sun sensitivity increase | Yes — SPF required | Yes — SPF required | Mild — SPF still advised |
| Result timeline | Weeks with consistent use | Weeks with consistent use | Gradual, may take longer |
AHAs: Surface Renewal for Dry and Dull Skin
Alpha hydroxy acids — glycolic acid and lactic acid being the most studied — are water-soluble and work primarily at the skin's surface. They loosen the upper layer of dead cells, which can improve the appearance of uneven tone, rough texture, fine lines, and hyperpigmentation over time. Glycolic acid has the smallest molecular size in this family, so it penetrates more readily; lactic acid is slightly larger, a bit milder, and also draws moisture into the skin, making it a common recommendation for drier complexions.
AHAs are generally well-tolerated at lower concentrations (around 5–10%) used a few times per week, though they do increase photosensitivity. Daily SPF use is not optional when incorporating these acids — it's essential. People with darker skin tones should also be aware that high concentrations or frequent use can sometimes trigger post-inflammatory hyperpigmentation, so starting low and slow is important.
Patch Test Before Committing
Before applying any new chemical exfoliant all over your face, test it on a small, discreet area — like behind the ear or inside the wrist — for a few days. This gives you a low-risk window to check for unexpected sensitivity before wider application. It's a simple step that's easy to skip and genuinely useful.
BHAs: Going Deeper for Oily and Congested Skin
Salicylic acid is the dominant BHA used in skin care, and its oil solubility is the key distinction. Because it can travel through sebum (the skin's natural oil), it gets inside pores rather than just working on the surface. This makes it particularly useful for blackheads, whiteheads, and acne-prone skin — conditions where congestion inside the follicle is the primary issue.
BHAs also have mild anti-inflammatory properties, which can make them less aggravating for skin that tends toward redness alongside breakouts. Concentrations typically range from 0.5% to 2% in over-the-counter products. Like AHAs, BHAs increase sun sensitivity and require consistent SPF protection. They can be drying if overused, so even oily skin types benefit from building up frequency gradually.
PHAs: The Gentler Option for Sensitive Skin
Polyhydroxy acids — including gluconolactone and lactobionic acid — have larger molecules than AHAs or BHAs. That size means they penetrate more slowly and superficially, which translates into significantly less irritation potential. Research suggests PHAs can provide similar surface-exfoliating benefits to AHAs while being far better tolerated by sensitive skin, rosacea-prone skin, and people who've found other acids too harsh.
PHAs also have humectant properties, drawing water to the skin much like lactic acid does. They're an increasingly popular choice for beginners or anyone who wants a lower-stakes introduction to chemical exfoliation. The trade-off is that results may be more subtle or take longer to appear compared to stronger acids. For sensitive or reactive skin types, though, that gentleness is often exactly the right call. If you're planning to add a PHA — or any new exfoliant — to your routine, a methodical introduction matters; the guide to switching products without triggering a reaction outlines a practical approach.
Choosing One (and Using It Safely)
The most common mistake with chemical exfoliants isn't picking the wrong one — it's using too much, too often, or stacking multiple acids at once. Overexfoliation leads to a compromised skin barrier: increased sensitivity, redness, and sometimes breakouts that look a lot like the problem you were trying to solve.
Start with one exfoliant, used once or twice per week, at a moderate concentration. Give your skin four to six weeks to adjust before increasing frequency. Moisturizer and SPF are non-negotiable partners. And if you're dealing with an underlying skin condition — eczema, rosacea, active acne — it's worth checking in with a dermatologist before introducing acids. Understanding your skin's baseline is also useful: dry and dehydrated skin respond differently to exfoliation, and knowing which you're dealing with shapes the choice.
This article is for general informational purposes only and is not a substitute for professional medical or dermatological advice. If you have a skin condition or specific concerns, consult a qualified healthcare provider.