Skin School · Resource Card

The Acid Family

Which exfoliating acid to start with, which to build to — ordered from gentlest to strongest.

"Acid" sounds harsh, but they range from barely-there gentle to deep and serious. The trick is starting at the kind end and only climbing once your skin is ready. Here's the whole family, in order.

The gentleness ladder

↑ Start here · gentlest, surface-levelstrongest, deepest ↓

PHA Polyhydroxy acid Best first acid

The kindest of all. Works on the surface, exfoliates slowly, and hydrates at the same time — its larger molecules can't penetrate deeply, so it's gentle by nature.

Best for: total beginners, sensitive or reactive skin, and as your daily gentle exfoliation in a toner.

Lactic Mild AHA

A gentle AHA that exfoliates and hydrates — larger-moleculed as AHAs go, so it's one of the mildest. Lovely for dry or dull skin.

Best for: dryness, dullness, a gentle step up from PHA once your skin is settled.

Mandelic Mild AHA

Another gentle AHA with the largest molecule in the AHA family, so it works slowly and evenly — kind to skin prone to pigmentation and a good fit for deeper tones.

Best for: uneven tone, congestion, sensitive skin that still wants an AHA.

Glycolic Strong AHA

The smallest, deepest-penetrating AHA — powerful for renewal and glow, but the most likely to sting or over-do it. Earn your way up to this one.

Best for: well-established skin chasing brightness and texture. Not a starting point.

BHA Salicylic acid

The odd one out: oil-soluble, so it gets inside the pore rather than just working on the surface. Decongesting and calming — a different job to the AHAs.

Best for: oily, congested or blemish-prone skin, and blackheads — once skin is well-established.

AHA vs BHA — the one distinction that matters

AHAs

Water-soluble · work on the surface

The big family — PHA, lactic, mandelic, glycolic. They're water-loving, so they work on the skin's surface, loosening dead cells to reveal smoother, brighter skin underneath.

Reach for an AHA when your goal is glow, texture, dullness or uneven tone.

BHA

Oil-soluble · works inside the pore

Mainly salicylic acid. It's oil-loving, so it can dissolve through sebum and work inside the pore — which is why it suits congestion and breakouts in a way AHAs can't match.

Reach for BHA when your goal is clearing congestion, blackheads or oily, blemish-prone areas.

How to use this in your routine In The Routine Bible, your acid lives on one leave-on night a week — never the same night as your retinoid. Start at the top of the ladder with a PHA, stay there until your skin is happy, and only climb when you're consistently comfortable. The acid is the last active to increase in strength, well into the later tiers. Gentle and consistent beats strong and sporadic, every time.

The non-negotiables

Never acid and retinoid on the same night. They're both serious actives — pair them and you overload the skin. Separate nights, always.

Always wear SPF. Acids make skin more sun-sensitive. Daily SPF 50+ isn't optional when you're exfoliating.

One acid at a time. Don't layer a glycolic toner under a lactic serum — pick one. More acid isn't more results, it's more irritation.

Let it dry, then carry on. Apply your leave-on acid, let it absorb, then your B/HA serum, mist and seal as normal.