Chemical exfoliants are the part of a skincare routine where confidence matters more than courage. If you know what each acid does and what your skin is trying to solve, you can pick a single product and be done. If you do not, you will buy all three, use none of them correctly, and convince yourself that exfoliation is too confusing to bother with.

This is the decoder. AHA, BHA, PHA, and which one is actually yours.

What "chemical exfoliation" means

Your skin replaces itself roughly every 28 days. Dead skin cells are normally shed continuously, but age, dryness, pollution, and slow cell turnover can leave them piled on the surface, which causes dullness, rough texture, clogged pores, and dark marks.

A chemical exfoliant dissolves the bonds (called desmosomes) that hold dead skin cells together, letting them shed faster. It replaces the more abrasive approach of a physical scrub, which tends to cause micro-tears on compromised skin. For Canadian winter-damaged barriers, chemical exfoliation is almost always the safer choice.

The three acid families do this by slightly different routes.

AHA: water-soluble surface exfoliants

AHA stands for alpha-hydroxy acid. The family includes:

• Glycolic acid: from sugar cane. Smallest molecule, penetrates deepest, strongest surface effect, highest irritation risk.
• Lactic acid: from fermented milk. Gentler than glycolic, also mildly hydrating.
• Mandelic acid: from bitter almond. Largest AHA molecule, gentlest, good for skin of colour (less pigmentation rebound).
• Tartaric, malic: less common, usually in acid blends.

AHAs dissolve the bonds between dead cells on the skin's surface. They are water-soluble, which means they do not penetrate into the pore; they work on the top layer.

Best for: dull skin, fine lines, sun damage, dry or combination skin. Not the first choice for active acne.

BHA: oil-soluble pore exfoliants

BHA stands for beta-hydroxy acid. In skincare, BHA almost always means salicylic acid, though some Korean products use betaine salicylate (a gentler derivative).

Salicylic acid is oil-soluble, which means it can dissolve through the sebum inside your pore and exfoliate from the inside. It is the dermatologist's first-line ingredient for non-cystic acne and blackheads. It also has mild anti-inflammatory action.

Best for: oily skin, blackheads, non-inflammatory acne, clogged pores, and anyone who can see congestion under their foundation. Not the first choice for dry skin or purely surface-level dullness.

Korean products that use BHA well: COSRX BHA Blackhead Power Liquid (4 percent betaine salicylate), Some By Mi AHA-BHA-PHA 30 Days Miracle Toner.

PHA: the gentle-cousin exfoliant

PHA stands for poly-hydroxy acid. The family includes:

• Gluconolactone: a larger molecule cousin of AHAs.
• Lactobionic acid: even larger, often used in medical-grade post-procedure products.

The key difference is molecule size. PHAs are much larger than AHAs, which means they cannot penetrate as deeply or as fast. They sit on the surface and exfoliate slowly, with less irritation and less photosensitivity.

They also have humectant properties, which makes them mildly hydrating - a unique trait among acids.

Best for: sensitive skin, rosacea-prone skin, first-time exfoliant users, and anyone whose skin has complained about AHAs in the past.

PHA (Gluconolactone): a large-molecule chemical exfoliant that works slowly and gently, with less photosensitivity than AHA or BHA. See full entry.

The decision tree

Pick one path based on what your skin is actually doing:

Your skin is dull and dry-prone

Use a lactic acid (AHA) product at 5 to 8 percent, once or twice a week, in the evening. Follow with a ceramide cream.

Your skin is oily with blackheads or mild acne

Use a salicylic acid (BHA) product at 0.5 to 2 percent, three to four nights a week, spot application on problem zones. Pair with niacinamide (see Niacinamide 101).

Your skin is sensitive, rosacea-prone, or new to exfoliation

Use a PHA product (gluconolactone or lactobionic acid) daily or every other day. Pair with centella for calming support.

Your skin has post-acne marks but is not actively breaking out

Use a mandelic acid (AHA) product, two to three nights weekly. Pair with vitamin C (morning - see Vitamin C Serum for Beginners) for combined brightening.

Frequency: less than you think

The most common mistake we see in customer emails is using an AHA toner every single night for the first two weeks. By day ten, the skin is stinging, flaking, and reactive to moisturizer.

The correct ramp:

• Week one: once, mid-week.
• Week two: twice, separated by two days.
• Week three: three times if skin is tolerating.
• Week four onward: two to three times weekly for AHA/BHA. Daily for PHA.

Exfoliation is the active that punishes over-enthusiasm the fastest. Slower is always safer.

Summer vs winter frequency

In a Canadian summer (see our summer routine guide), consider pulling back AHA/BHA frequency by 30 to 50 percent. Photosensitivity and increased sebum production mean you need less exfoliation and more sunscreen.

In winter, when sebum drops and dead skin accumulates faster, exfoliation becomes more useful. Move to two to three times weekly from December through March if your barrier is stable.

What not to layer with your acid

On the night you use an acid:

• Skip retinol. Choose one or the other for that evening.
• Skip vitamin C serums; save those for mornings.
• Use a hydrating essence and ceramide cream after the acid.

The next morning, sunscreen is non-negotiable. AHA and BHA both increase UV sensitivity for up to a week after application. PHA does so less, but do not treat that as permission to skip SPF.

Korean acid products we reach for

For AHA: Some By Mi AHA-BHA-PHA 30 Days Miracle Toner (a blend, gentle enough for most).

For BHA: COSRX BHA Blackhead Power Liquid.

For PHA: Isntree PHA 5.5 Refreshing Toner or Benton PHA Peeling Gel.

Start with one. Use it consistently for four weeks. Judge by photographs at week one and week four, not by how your skin feels at day three.

The summary

Acids are not scary. They are specific. Pick the family that matches your skin type, start at low frequency, and protect with sunscreen the next day. In six weeks, your skin will be brighter, smoother, and less clogged than any routine without an exfoliant can achieve. In eight weeks, you will have earned the right to experiment with frequency and combinations.

One acid. Done correctly. Better than three acids done carelessly.