Glycolic acid is the most researched AHA in skincare. It's also the one most likely to create new dark spots on melanin-rich skin. The reason comes down to one thing: molecular size.
How AHAs work — and why penetration speed matters
Alpha hydroxy acids (AHAs) exfoliate by loosening the bonds between dead skin cells, allowing them to shed and revealing smoother skin underneath. All AHAs do this — but they don't all do it at the same speed or depth.
The key variable is molecular size. Smaller molecules penetrate faster and deeper. Larger molecules penetrate more slowly and more evenly across the skin surface. For most skin types, speed of penetration is not a major concern. For melanin-rich skin, it's the difference between an ingredient that helps and one that triggers a new problem.
Why glycolic acid is risky for deeper skin tones
Glycolic acid has the smallest molecular size of any AHA. This is what makes it so effective — it penetrates quickly, works deeply, and delivers fast results. For lighter skin tones, this is usually fine. For melanin-rich skin, this speed often causes a problem.
When glycolic acid penetrates quickly, it can cause enough inflammation to trigger the skin's pigment response. Melanocytes — the cells that produce melanin — interpret inflammation as damage and produce excess pigment to protect the skin. The result is post-inflammatory hyperpigmentation (PIH): a new dark mark created by the product that was supposed to clear old ones.
This is one of the most common experiences in the melanin-rich skincare community: trying a glycolic acid product that everyone online recommends and ending up with darker skin, not lighter. It's not a reaction to the product itself. It's a predictable biological response to a formula that wasn't designed with melanin-rich skin in mind.
Important: This risk increases with concentration. High-concentration glycolic acid peels — especially at-home versions — are one of the most common causes of new dark spots on deeper skin tones. If a product stings beyond a mild tingle, that is your skin's inflammatory response activating. Stop use immediately.
Why mandelic acid is different
Mandelic acid is derived from bitter almonds and has a significantly larger molecular structure than glycolic acid. This larger size means it penetrates the skin more slowly and more evenly — effective exfoliation without the aggressive spike that triggers PIH.
Because it moves more slowly, mandelic acid has more time to work uniformly across the skin surface rather than diving deep into some areas while barely touching others. This results in more predictable, more even exfoliation — which is why it is consistently recommended for melanin-rich and sensitive skin types by dermatologists who specialize in skin of color.
A clinical study published in the Journal of the American Academy of Dermatology assessed mandelic acid in subjects with melasma — a form of hyperpigmentation particularly common in deeper skin tones. After 4 weeks of treatment with a 10% mandelic acid formulation, subjects showed a 50% improvement in melasma severity with minimal side effects.
Journal of the American Academy of Dermatology →Side-by-side comparison
| Glycolic Acid | Mandelic Acid | |
|---|---|---|
| Molecular size | Smallest AHA | Largest AHA |
| Penetration speed | Fast, deep | Slow, controlled |
| PIH risk on melanin-rich skin | High | Low |
| Irritation potential | Higher | Lower |
| Suitable for sensitive skin | Not recommended | Yes |
| Recommended for deeper skin tones | Use with caution | Yes |
What about lactic acid?
Lactic acid sits between glycolic and mandelic in terms of molecular size — larger than glycolic but smaller than mandelic. It is gentler than glycolic acid and can work for some people with melanin-rich skin, particularly at lower concentrations. However, it carries more PIH risk than mandelic acid, and for skin that is reactive or already dealing with active dark spots, mandelic acid remains the safer choice.
How NO FLARE™ uses mandelic acid
AVA Body Toner uses mandelic acid at a pH of 3.73 — the optimal range for AHA efficacy. The formula also includes Centella Asiatica Extract, Aloe Barbadensis Leaf Juice, Panthenol, and Allantoin to calm the skin's response during exfoliation and minimize any residual inflammation.
AVA is designed to be used as Step 1, followed by NORA Dry Oil (Step 2), which uses LHA — an oil-soluble exfoliant that works inside the follicle — to address ingrown hairs and KP at their source while supporting the skin barrier with Ceramide NP and Ceramide AP.
Both products are fragrance-free, dermatologically tested, and formulated specifically for melanin-rich and sensitive skin.
Summary
- Glycolic acid penetrates fast and deep — increasing PIH risk on melanin-rich skin.
- Mandelic acid penetrates slowly and evenly — effective exfoliation with a lower risk of triggering new dark spots.
- For skin that marks easily, the speed of penetration matters as much as the concentration.
- Mandelic acid is consistently recommended by dermatologists who specialize in skin of color.
- If a product stings or causes visible redness, stop use — this is the inflammatory response that causes PIH.
AVA uses mandelic acid at pH 3.73 — formulated for melanin-rich and sensitive skin.
Shop AVA on Amazon →