Science Explainer Series

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Skin 101 · Oswego, IL

The Skincare Acids Guide

Seven acids, seven jobs

A plain-language breakdown of what each active actually does, who it's best for, and how they're typically used — so you can ask for the right thing by name.

Actives covered in this guide

2–3×

Typical starting frequency per week

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⚠ Before you start

Acids are active ingredients — they change your skin, which means they can also irritate it if you move too fast. Strengths, frequencies, and pairings below are general starting points, not a personalized plan. Patch test anything new, and check with your provider before combining several actives at once.

Skincare acids guide — lactic, glycolic, mandelic, hyaluronic, azelaic, salicylic, and vitamin C with benefits and best-for labels

Full depth reference — tap to zoom on mobile, or save for your consult

1Skin 101

AHA vs. BHA, In Plain English

AHAs (lactic, glycolic, mandelic) are water-soluble and work on the skin's surface — great for texture, tone, and brightness. BHA (salicylic acid) is oil-soluble, so it can actually get inside the pore to clear out oil and debris. That's why oily, acne-prone skin usually reaches for a BHA, while dry or sun-damaged skin usually starts with an AHA.

2Skin 101

The Gentle Exfoliants (AHAs)

From gentlest to most potent

AHA · 5–10%

Lactic Acid

Gentle exfoliation, brightening
Good first acid for sensitive or dry skin

Best for: Keratosis pilaris

Typical use: 2–3×/week, PM

AHA · 5–10%

Glycolic Acid

Renews skin, boosts glow
Smallest AHA molecule — most potent, most irritating

Best for: Dark spots

Typical use: 2–3×/week, PM

AHA · up to 10%

Mandelic Acid

Gentle exfoliation, evens tone
Safest AHA for deeper skin tones

Best for: Sensitive skin

Typical use: 2–4×/week, AM or PM

3Skin 101

Hydration, Calming & Pore Care

Humectant

Hyaluronic Acid

Deep hydration, plumps skin
Apply to damp skin, seal with moisturizer

Best for: Dry, dehydrated skin

Typical use: Daily, AM + PM

10–20%

Azelaic Acid

Reduces redness, evens tone
One of the few actives safe for daily use

Best for: Rosacea

Typical use: 2–3×/week → daily

BHA · 0.5–2%

Salicylic Acid

Unclogs pores, controls oil
Oil-soluble — cleans inside the pore

Best for: Acne-prone skin

Typical use: 3–5×/week, PM

4Skin 101

The One That Doesn't Follow the Rules

Vitamin C (ascorbic acid) is an antioxidant, not an exfoliant. At 10–20%, used daily in the morning under SPF, it helps fight free-radical damage and boosts your sunscreen's protection — which is why it's the one acid on this list that belongs in your AM routine, not your PM one. Save the exfoliating acids for night.

5Skin 101

What Pairs Well — And What Doesn't

The combinations that work together, the ones that cancel each other out, and how to build a routine that doesn't fight itself.

Active	Pairs well with	Avoid mixing with
Lactic Acid	Hyaluronic acid, moisturizer after	Other AHAs/BHAs same night, retinol same night
Glycolic Acid	Hyaluronic acid, niacinamide (alternate nights)	Vitamin C same session, retinol same night
Mandelic Acid	Salicylic acid (alternate days), hyaluronic acid	Other AHAs same session, physical scrubs
Hyaluronic Acid	Everything — layers under any acid	Nothing — universally compatible
Azelaic Acid	Vitamin C (AM), hyaluronic acid, niacinamide	Salicylic acid same session
Salicylic Acid	Hyaluronic acid, niacinamide	Vitamin C same session, retinol same night
Vitamin C	Vitamin E, ferulic acid, SPF over top	AHAs/BHAs same session — destabilizes it

6Skin 101

Build a Routine That Doesn't Fight Itself

1
Start Slow
- — One new acid at a time
- — 2–3×/week for the first month
- — Watch for redness or peeling
2
Separate AM/PM
- — Vitamin C + SPF in the morning
- — Exfoliating acids at night
- — Hyaluronic acid fits either
3
Always Moisturize
- — Acids work best on a hydrated barrier
- — Seal actives with a moisturizer
- — Don't skip SPF the next day

7Skin 101

If Your Skin Is Sensitive

Start with mandelic acid or azelaic acid — both are gentler entry points with lower irritation potential, and azelaic acid is one of the few actives that can build up to daily use.

Persistent redness, burning, or peeling that doesn't settle within a few days isn't "purging" — pause and check in with your provider before continuing.

How We Think About It at Hello Gorgeous

Acids are powerful, but more isn't better — the right acid, at the right strength, used consistently, beats a five-step routine that irritates your skin. If you're not sure where to start, that's exactly what a consult is for. Still family-owned, still honest, still in your corner.