Post-Acne Marks vs True Hyperpigmentation: How to Tell the Difference (and Treat Each)

When I started developing marks on my cheeks and chin in my early forties, I spent several months treating what I now know were post-acne marks as if they were sun hyperpigmentation. The treatments were not wrong in principle – niacinamide, vitamin C, SPF – but the approach was too generalised to be effective, because the two types of discolouration have different causes, different depths, and different response timelines. Understanding the distinction did not just improve my results; it changed which products I reached for and in which order.

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Post-Acne Marks: The Two Types and How to Tell Them Apart

Post-acne discolouration is divided into two distinct types based on the mechanism that produces it. Post-inflammatory erythema, referred to as PIE, is the reddish or pinkish flat discolouration that follows a breakout. It is caused by dilated and damaged capillaries in the dermis – the response to the inflammation of the original spot – and it is primarily vascular rather than melanin-based. Under a glass pressed against the skin (blanching test), PIE will lighten or disappear, because the colour comes from blood within vessels that can be temporarily emptied by pressure.

Post-inflammatory hyperpigmentation, referred to as PIH, is a different type of mark. It is brown or grey-brown in colour and is caused by the overproduction of melanin triggered by the inflammation of a breakout. PIH is melanin-based rather than vascular, and it will not lighten under pressure in the blanching test. It tends to affect darker skin tones more significantly than lighter ones – melanocytes (the cells that produce melanin) in deeper skin tones produce more melanin in response to inflammatory triggers.

The distinction matters because the most effective treatment targets differ. PIE responds best to ingredients that address vascular issues and support skin recovery – niacinamide, centella asiatica, azelaic acid at lower concentrations. PIH responds to melanin-inhibiting actives – niacinamide, azelaic acid, kojic acid, vitamin C, and in more persistent cases, prescription-strength treatments. There is meaningful overlap, which is why both types often improve on the same routine – but understanding which you are treating allows a more targeted approach.

Sun Hyperpigmentation – Why It Is Different From Both

Hyperpigmentation from UV exposure – the flat brown patches that develop on the forehead, cheeks, and upper lip – is distinct from post-acne marks in its origin and, often, in its depth. Sun hyperpigmentation involves melanocytes that have been chronically stimulated by UV radiation over time, producing melanin deposits that can sit at the dermal-epidermal junction rather than purely in the epidermis. This depth makes it slower to respond to topical treatment than epidermal post-acne marks.

The non-negotiable in managing sun hyperpigmentation is daily broad-spectrum SPF 50 or higher. Without consistent UV protection, any topical brightening treatment is working against ongoing melanin stimulation – the marks will continue to darken faster than any ingredient can fade them. SPF is not the finishing step in a brightening routine; it is the foundation that makes every other step viable.

How I Approach Treatment for Each Type

For PIE, the most consistent results in my own skin have come from niacinamide at 5% used twice daily, combined with centella asiatica – both of which support vascular repair and reduce the redness associated with capillary damage. Azelaic acid at 10%, used on alternate evenings, added an additional layer of anti-inflammatory action. The marks that I had been trying to fade for months began to visibly improve within six weeks of this targeted approach.

For PIH and sun hyperpigmentation, the routine is similar but with the addition of vitamin C in the morning – a stable, well-formulated ascorbic acid serum at 10 to 15% – as a melanin inhibitor and antioxidant that addresses both new pigment formation and existing deposits over time. The combination of morning vitamin C, daily niacinamide, evening azelaic acid, and consistent SPF 50 is the protocol I have found most effective and best tolerated on dry, sensitive skin.

One point worth emphasising: the temptation to add more actives when marks are not fading quickly enough is understandable, but consistency at a moderate intensity outperforms aggressive treatment in most cases. High-concentration acids and prescription brighteners can deliver faster results, but they also carry a higher risk of post-inflammatory hyperpigmentation themselves if they irritate the skin. The irony is that over-treating hyperpigmentation can produce more hyperpigmentation.

Frequently Asked Questions

How do I know if my marks are PIE or PIH?

The blanching test is the most reliable home method: press a clean glass firmly against the mark and hold it for a few seconds. If the mark fades or disappears under pressure, it is likely PIE (vascular). If it remains unchanged, it is likely PIH (melanin-based). Colour is also a guide – pink and red marks are typically PIE; brown and grey-brown marks are typically PIH.

Will post-acne marks fade on their own?

PIE typically fades more quickly than PIH when left alone – the damaged capillaries repair over time, and the redness resolves. Without active treatment, this can take six to twelve months. PIH is more persistent and often requires consistent use of melanin-inhibiting actives to fade within a reasonable timeframe. Both types are significantly slowed by unprotected UV exposure.

Can I use retinol for post-acne marks?

Yes – retinol accelerates cell turnover, which helps bring pigmented cells to the surface more quickly and reduces the time marks remain visible. It is more effective for PIH than for PIE. The caveat for dry, sensitive skin is that retinol needs to be introduced very gradually – the irritation it can cause in an unsupported routine can produce new post-inflammatory hyperpigmentation of its own, which counteracts the purpose. Barrier repair before retinol introduction is the approach I follow.

Does SPF really make a difference for existing marks?

Yes – significantly. UV exposure stimulates melanin production and darkens existing hyperpigmentation directly. Without daily SPF 50 or higher, the marks being treated with actives are simultaneously being stimulated to darken. Consistent SPF is the single most impactful change for anyone managing hyperpigmentation, and the one most commonly underestimated.

The serum I reached for when working through my own post-acne marks was the Axis-Y Dark Spot Correcting Glow Serum — it combines several of the brightening mechanisms covered above in a single formula, and sits under SPF without pilling. I have written a more detailed breakdown of it separately if you want the full picture on the formulation.