On this page
- What causes hyperpigmentation?
- Why deeper skin tones hold pigment longer
- Post-inflammatory hyperpigmentation: the mechanism
- PIH versus melasma: they are not the same problem
- Why aggressive exfoliation backfires
- Sun protection, including through an Ontario winter
- Realistic timelines
- Frequently asked questions
What causes hyperpigmentation?
Hyperpigmentation happens when melanocytes — the pigment-producing cells in the lower epidermis – overproduce melanin in response to a trigger, and that pigment is deposited into the surrounding skin. The main triggers are inflammation, ultraviolet and visible light, hormones, friction and heat. In melanin-rich skin the melanocytes are more reactive and produce more pigment per stimulus, so the same trigger leaves a darker, longer-lasting mark.
Why deeper skin tones hold pigment longer
Everyone has roughly the same number of melanocytes. The difference across the Fitzpatrick scale is how much melanin those cells produce, what type, and how it is packaged and distributed.
In Fitzpatrick IV–VI skin, melanocytes are larger and more metabolically active, and they distribute melanosomes — the packets that carry pigment — more widely through the surrounding cells. It is an effective UV defence system. It also means the same cells respond vigorously to any inflammatory signal, so a spot, an ingrown hair, a bug bite or an over-enthusiastic exfoliation session can each leave a mark that takes many months to clear.
Depth is the other factor. When inflammation reaches deep enough, pigment drops from the epidermis into the dermis below — dermal pigmentation, which appears grey-blue rather than brown. Epidermal pigment sheds with natural turnover in months. Dermal pigment has no such exit route and is far more stubborn.
Post-inflammatory hyperpigmentation: the mechanism
PIH is a wound response. Inflammation — from acne, eczema, a burn, friction, a cosmetic procedure — releases inflammatory mediators including prostaglandins and cytokines. These directly stimulate melanocytes to increase melanin production and transfer it into nearby keratinocytes.
Two consequences follow, and they explain most of what confuses people about PIH:
The mark appears where the inflammation was. PIH maps precisely onto old lesions. If your marks trace the pattern of last month’s breakout, that is PIH.
Every new inflammatory event restarts the clock. Picking a spot, scrubbing at a mark or using a product that stings is not neutral — it re-triggers the same cascade. Most stubborn PIH is not one event; it is a series of them.
PIH versus melasma: they are not the same problem
They are frequently confused and treated identically, which is why one of them so often fails to improve.
| Post-inflammatory hyperpigmentation | Melasma | |
| Cause | A specific inflammatory event | Hormonal, plus UV, visible light and heat |
| Pattern | Matches where the injury was | Symmetrical patches — cheeks, upper lip, forehead |
| Edges | Follows the original lesion shape | Diffuse, irregular, blotchy |
| Triggers | Acne, injury, procedures, friction | Pregnancy, oral contraceptives, sun, heat |
| Course | Fades over months once the trigger stops | Chronic and relapsing; managed, not cured |
Melasma is a management condition. It flares with heat and light — including a hot kitchen, a sauna, or a steamy treatment room — and relapses when protection lapses. Expecting it to be permanently “removed” leads people into progressively more aggressive treatments, which is the worst possible direction, because melasma is notoriously heat- and irritation-sensitive.
Why aggressive exfoliation backfires
The intuition is that pigment sits on top and should be sanded off. On melanin-rich skin this is often counterproductive.
Aggressive physical scrubs, high-strength acids used too frequently, and heat-based devices all create inflammation. Inflammation is the exact trigger for melanocyte activation. So the treatment intended to remove pigment stimulates production of more — and because the melanocytes are already primed, the rebound can be worse than the original mark.
This is the single most common reason pigmentation treatment fails on deeper skin. The effective approach is slow and unglamorous: reduce the trigger, protect obsessively, and use gentle, sustained pigment-inhibiting actives — niacinamide, azelaic acid, tranexamic acid, well-formulated vitamin C, and where appropriate, prescription options under supervision. Gentler acids such as mandelic and lactic are generally preferred over high-strength glycolic, as covered in our breakdown of exfoliation methods.
Sun protection, including through an Ontario winter
UV is the accelerant for every form of pigmentation. Melanin provides meaningful but incomplete natural protection — roughly equivalent to a low SPF — which is not enough to prevent pigment darkening.
Visible light matters too, and this is where most sunscreen advice falls short for deeper skin. High-energy visible light penetrates deeper than UVB and induces pigment darkening that persists longer, particularly in Fitzpatrick IV–VI skin. Conventional clear sunscreens do not block it. Tinted formulas containing iron oxides do, which is why a tinted mineral sunscreen is genuinely more effective for pigment control than an untinted one at the same SPF.
Through a London winter this still applies. UV persists through cloud, snow reflects a substantial proportion of it upward, and winter sun sits at an angle that hits the face directly.
Realistic timelines
Epidermal PIH fades over roughly three to twelve months with good protection and consistent actives. Dermal pigmentation takes longer and may not fully resolve. Melasma improves with treatment and relapses without maintenance.
Anything promising to clear pigmentation in two weeks is either using something unsafe or describing surface exfoliation that will rebound.
Because pigment and texture are separate problems, work out which you have before treating — our guide to the four acne scar types covers that test — and if you are seeing new spots after starting a treatment, check whether it is purging or a reaction before adding anything else.
Frequently asked questions
How long does post-inflammatory hyperpigmentation take to fade? Three to twelve months for epidermal pigment with consistent sun protection. Deeper dermal pigment takes longer.
Is hyperpigmentation permanent? Usually not, but it can be very long-lasting — especially dermal pigment. Repeated re-triggering is what makes it look permanent.
Can I use hydroquinone? It is effective but should be used under professional supervision and in limited courses, as prolonged unsupervised use carries risks.
Does vitamin C help? Yes — it inhibits tyrosinase, the enzyme central to melanin synthesis, and adds antioxidant protection. It works best alongside daily sunscreen rather than instead of it.