Unit 4 · Azelaic acid, thresholds & combining
The acid outside the AHA/BHA/PHA system, and the limits everyone works within
Azelaic acid sits outside the classification covered in Units 2 and 3, yet addresses three of the most common presenting concerns at once. Concentration thresholds and scope of practice then set the hard limits on what any practitioner may actually do with any acid in this module.
Learn · Azelaic acid
One acid, three overlapping clinical problems
Azelaic acid is one of the most clinically versatile topical actives in aesthetic medicine, yet it is often underutilised, particularly outside dermatology. It is a dicarboxylic acid — not technically an AHA or a BHA — with a combination of mechanisms that make it particularly valuable for three commonly co-occurring conditions: hyperpigmentation, rosacea and acne.
- Source
- Naturally occurring in grains (wheat, rye, barley); produced by Malassezia yeast; synthetically manufactured for cosmetic use
- Molecular weight
- 188 Da
- OTC range (AU)
- Up to 10%
- Prescription range
- 15–20% (Skinoren, Finacea)
- Actions
- Tyrosinase inhibitor, keratolytic, anti-inflammatory, antibacterial, antikeratinising
Tyrosinase inhibition: azelaic acid selectively inhibits tyrosinase in hyperactive melanocytes — reducing melanin synthesis specifically in dyspigmented cells without affecting normally pigmented skin.
Its anti-inflammatory action inhibits reactive oxygen species generation by neutrophils, reducing the inflammatory component of acne and rosacea. Its antibacterial action inhibits protein synthesis in C. acnes at therapeutic concentrations — comparable to topical antibiotics in some studies, without the antibiotic resistance risk. Its keratolytic action normalises abnormal keratinisation of the follicular epithelium, addressing comedone formation similarly to, but less potently than, retinoids.
Azelaic acid's tyrosinase inhibition is described as "selective" because:
Select an option to commit. The reasoning appears afterwards.
Azelaic acid inhibits tyrosinase specifically in hyperactive melanocytes, reducing melanin synthesis in dyspigmented cells while leaving normally pigmented surrounding skin untouched. This selectivity is the key advantage over some other tyrosinase inhibitors.
It is also why azelaic acid does not carry hydroquinone's paradoxical depigmentation risk — the mechanism only engages where melanocyte activity is already abnormal, which is exactly the property that makes it particularly safe and effective across Fitzpatrick IV–VI skin.
Rosacea (papulopustular): a registered indication in Australia at prescription strength (15–20%). Reduces both inflammatory papules and erythema — one of the few actives that addresses the inflammatory component of rosacea effectively, and usable in skin that would not tolerate retinoids or AHAs.
Hyperpigmentation, all phototypes: selective tyrosinase inhibition makes azelaic acid particularly safe and effective in Fitzpatrick IV–VI. Unlike hydroquinone, it does not cause paradoxical depigmentation of surrounding normal skin and does not carry a bleaching risk.
Acne in sensitive or rosacea-prone skin: anti-inflammatory and antibacterial properties make it one of the few acne actives also appropriate for rosacea-prone skin, where BHAs and retinoids might be too stimulating.
Azelaic acid is one of the most recommended alternatives to hydroquinone in skin of colour for three reasons: it does not bleach normally pigmented skin — only hyperactive melanocytes are affected; it has anti-inflammatory activity that reduces the PIH-driving inflammatory signal; and it is available OTC at 10% without a hydroquinone prescription and the regulatory concerns associated with extended hydroquinone use. Combining azelaic acid (10%) with niacinamide (5–10%) and SPF 50+ targets the PIH cycle at three independent points: melanin synthesis, melanosome transfer and UV-induced melanocyte activation.
Predict · OTC vs prescription concentration
The same active, two very different regulatory pathways
Azelaic acid is available both over the counter and by prescription in Australia — but not at the same strength. Before reading the next section, commit to a position.
A client asks whether she can simply buy a 15% azelaic acid product over the counter instead of seeing a prescriber. Is that available in Australia?
Hold your answer before you open this. The value is in having committed to a position on the regulatory boundary first.
No. In Australia, azelaic acid is available OTC only up to 10%. The 15–20% strength sits in the prescription range and requires a prescriber.
This is not a minor labelling distinction — it is the line between a product a beauty therapist can sell over the counter and one that requires a prescription pathway, and it sets up the scope-of-practice question the next section addresses directly.
Learn · Concentration thresholds
OTC, professional and prescription — the TGA lines
In Australia, the Therapeutic Goods Administration (TGA) regulates the concentrations at which acid-based products can be sold over the counter (OTC) versus dispensed through professional channels or prescribed. Understanding these thresholds is clinically important — they inform the advice you can give and the products you can recommend.
| Acid | OTC limit (AU) | Professional / clinic use | Prescription | Key safety consideration |
|---|---|---|---|---|
| Glycolic acid | ≤10% (pH ≥3.5) | 10–70% | Not applicable | High irritation at >10%; professional peels require training and neutralisation protocols |
| Lactic acid | ≤10% | 10–50% | Not applicable | Better tolerated than glycolic at equivalent %; neutraliser required for professional strengths |
| Mandelic acid | ≤10% | 10–40% | Not applicable | Self-neutralising — lower risk profile for professional use; broad dark-skin safety profile |
| Salicylic acid | ≤2% | 10–30% | Not applicable | Self-neutralising; aspirin hypersensitivity cross-reactivity; avoid at professional strengths in pregnancy |
| Gluconolactone / lactobionic | No specific limit; widely OTC | Up to 14–15% | Not applicable | Lowest risk profile of all exfoliating acids; pH-controlled products self-limiting |
| Azelaic acid | ≤10% | Not typically a peel agent | 15–20% (Skinoren, Finacea) | Well tolerated; no neutralisation required; prescription products require appropriate scope of practice |
| Tretinoin (retinoic acid) | Not OTC in AU | Not applicable | 0.025–0.1% prescription (S4) | Prescription only; requires clinical assessment; refer to Module 03.04 for full retinoid guidance |
In Australia, the authority to perform professional-strength chemical peels varies by state and territory and by professional registration. Beauty therapists are generally limited to lower-strength OTC products under state-based regulations. Registered nurses, enrolled nurses, and other AHPRA-registered practitioners operating within their scope of practice may apply higher concentrations under appropriate supervision or within their defined scope. Always verify your specific scope of practice with your registration body and employer before applying any professional-strength acid treatment.
A beauty therapist wants to offer a 20% azelaic acid peel in clinic because a client has read about it online. The correct position is:
Select an option to commit. The reasoning appears afterwards.
Azelaic acid's OTC limit in Australia is 10%. The 15–20% range is prescription strength, and prescription products require appropriate scope of practice. Beauty therapists are generally limited to lower-strength OTC products under state-based regulations — a 20% product falls outside that scope regardless of client interest or the product's tolerability profile.
Registered nurses, enrolled nurses and other AHPRA-registered practitioners operating within their defined scope may apply higher concentrations under appropriate supervision. The governing question is never "will the client tolerate this" — it is "am I authorised to apply this." Always verify scope of practice with your registration body and employer before proceeding.
Learn · Combining acids safely
Combinations can multiply benefit — or multiply risk
Acid combinations can enhance efficacy, but they also multiply the risk of barrier disruption, over-exfoliation and irritation if not managed carefully. The following principles guide safe acid combination in home-use and clinical contexts.
A patient using azelaic acid for hyperpigmentation wants to add niacinamide to her routine. Should these be separated, or can they be applied together?
Hold your answer before you open this. The value is in having committed to a position on compatibility first.
They can be stacked freely — the combination is synergistic, not merely compatible. Azelaic acid and niacinamide work through complementary pigmentation pathways: tyrosinase inhibition and melanosome transfer inhibition.
This is an excellent protocol for PIH in darker skin types specifically because it attacks the pigmentation problem from two independent mechanisms at once, rather than relying on a single pathway.
A patient wants to use a glycolic acid product and a retinoid on the same night for faster results. The correct guidance is:
Select an option to commit. The reasoning appears afterwards.
Both AHAs/BHAs and retinoids disrupt the skin barrier. Combining them in the same session increases irritation risk substantially, so the standard guidance is to use the acid one night and the retinoid the next — separating them onto alternating nights rather than stacking or banning either outright.
Advanced, well-acclimatised users can sometimes layer the two after a period of tolerance has been established, but that is a progression from the alternating-night starting point, not the default recommendation for a patient introducing this combination for the first time.
Learn · Acid combination guide
Reference: what combines, what needs timing, what to avoid
| Combination | Compatibility | Guidance |
|---|---|---|
| AHA + BHA (e.g. glycolic + salicylic) | Compatible | Complementary mechanisms — glycolic for surface texture, salicylic for follicular congestion. Monitor for over-exfoliation in sensitive skin. |
| AHA + PHA (e.g. lactic + gluconolactone) | Compatible | PHA provides gentle exfoliation; AHA adds depth. Suitable for dry or sensitive skin wanting exfoliation without harsh effects. |
| AHA + niacinamide | Compatible | Niacinamide supports the barrier after AHA use. Apply niacinamide after the acid step has dried, allowing 20–30 minutes if pH-sensitive stacking is a concern. |
| AHA + vitamin C (LAA) | Timing matters | Vitamin C requires pH <3.5. Applying after an AHA is fine, since the AHA has lowered skin pH. AM vitamin C, PM AHA is the cleanest approach. |
| AHA/BHA + retinoid, same night | Separate nights | Both disrupt the barrier; combining substantially increases irritation risk. Use the acid one night, the retinoid the next. |
| AHA + benzoyl peroxide | Separate steps | Benzoyl peroxide can degrade AHA-adjacent actives. Apply at different times of day and ensure concurrent barrier support for dryness. |
| Multiple high-% AHAs simultaneously | Avoid | Stacking glycolic, lactic and mandelic at full concentrations simultaneously risks severe over-exfoliation. Choose one AHA and rotate, or use a formulated combination product. |
| Azelaic acid + niacinamide | Synergistic | Complementary pigmentation pathways — tyrosinase inhibition plus melanosome transfer inhibition. An excellent protocol for PIH in darker skin types. |
| BHA + mandelic acid | Compatible | Salicylic (follicular) with mandelic (surface antibacterial and exfoliation) — a useful combination for inflammatory acne in darker skin types. |
Over-exfoliation is more common than many patients realise, particularly when using multiple exfoliating actives or professional-strength products without adequate guidance. Warning signs: persistent redness or stinging, skin that feels tight and shiny rather than dewy, increased sensitivity to previously well-tolerated products, sudden breakouts, and unusual flakiness or peeling.
If over-exfoliation is suspected: stop all exfoliating actives, revert to barrier repair (gentle cleanser, panthenol, ceramide moisturiser, SPF), and allow at least 1–2 weeks of recovery before reintroducing exfoliants at a lower frequency or concentration.
Learn · Quick reference
Acid × condition matrix
| Acid | Photoageing / texture | Acne / oily / comedonal | Hyperpigmentation / PIH | Sensitive / rosacea | Fitzpatrick IV–VI | Post-procedure | Dry / dehydrated |
|---|---|---|---|---|---|---|---|
| Glycolic acid | ✓✓✓ strong / first-line | ✓ adjunct | ✓✓ good match | ✗ generally unsuitable | Caution — low % only | Phase 3+ only | Caution — hydrate concurrently |
| Lactic acid | ✓✓ good match | ✓ adjunct | ✓✓ good match | Caution — low % | ✓✓ good match | Caution — phase 3 | ✓✓✓ strong / first-line |
| Mandelic acid | ✓✓ good match | ✓✓ good match | ✓✓ good match | ✓✓ good match | ✓✓✓ strong / first-line | Caution — phase 3 | Caution — suitable / adjunct |
| Salicylic acid | Caution — surface only | ✓✓✓ strong / first-line | ✓✓ good match | Caution — low % | ✓✓ good match | Phase 3+ | Caution — hydrate concurrently |
| Gluconolactone | ✓✓ good match | ✓ suitable / adjunct | ✓ suitable / adjunct | ✓✓✓ strong / first-line | ✓✓✓ strong / first-line | ✓✓✓ strong / first-line | ✓✓ good match |
| Lactobionic acid | ✓ suitable / adjunct | ✓ suitable / adjunct | ✓ suitable / adjunct | ✓✓✓ strong / first-line | ✓✓✓ strong / first-line | ✓✓✓ strong / first-line | ✓✓✓ strong / first-line |
| Azelaic acid | ✓ suitable / adjunct | ✓✓✓ strong / first-line | ✓✓✓ strong / first-line | ✓✓✓ strong / first-line | ✓✓✓ strong / first-line | Phase 2–3 | ✓✓ good match |
✓✓✓ = strong match / first-line · ✓✓ = good match · ✓ = suitable / adjunct · Caution = conditional use · ✗ = generally contraindicated or ineffective. Post-procedure phases: phase 1 = re-epithelialisation (days 1–7); phase 2 = proliferation (days 4–21); phase 3 = remodelling (week 3+).
Unit 4 summary
Clinical takeaways
- Azelaic acid sits outside the AHA/BHA/PHA system and does three jobs at once. Tyrosinase inhibition, anti-inflammatory action, antibacterial action and keratolytic action together address pigmentation, rosacea and acne through distinct, complementary mechanisms.
- Concentration limits are hard regulatory lines, not general guidance. TGA OTC limits — for example salicylic acid at ≤2%, azelaic acid at ≤10% — sit below professional and prescription ranges for defined safety reasons.
- Scope of practice determines who may apply which concentration, not tolerability. Beauty therapists are generally limited to OTC-strength products; higher concentrations require AHPRA registration and confirmed scope, verified against your registration body and employer.
- Combining acids multiplies risk as often as it multiplies benefit. Some pairings are compatible or synergistic — azelaic acid with niacinamide — some need timing separation — AHA/BHA with a retinoid — and some, like stacking multiple high-percentage AHAs, should be avoided altogether.
This module is in draft. If anything here reads as unclear, incomplete or clinically contestable, record it in the review form.