Post-inflammatory hyperpigmentation: what it is, why it happens, and how we treat it

The spot healed weeks ago. What is left is a flat brown mark exactly where it was, and it has not moved since. Makeup covers it. Nothing else seems to.

Patients often arrive convinced this is scarring, and braced for the answer that it is permanent. It usually isn't. What they have is post-inflammatory hyperpigmentation, and the distinction matters, because a scar is a change in the structure of the skin and this is not. Run a finger across it and the surface is smooth. Nothing was lost. Something was only left behind.

What post-inflammatory hyperpigmentation actually is

Inflammation is not a quiet process. When skin is injured or irritated, it releases a cascade of signals: inflammatory cytokines, prostaglandins, reactive oxygen species.¹ Those signals do many useful things, and they also reach melanocytes, the pigment-producing cells sitting at the base of the epidermis. Melanocytes respond the only way they know how. They make more melanin.

That melanin gets handed off to surrounding keratinocytes and rises with them as the skin turns over. The result is a flat patch of extra pigment in the precise footprint of whatever caused the inflammation. Acne is the most common trigger by a wide margin, but eczema, an insect bite, a scratch, a burn, a chemical peel and an overaggressive laser pass all produce the same response.¹

Which is worth pausing on. The skin is not malfunctioning here. It is doing exactly what it evolved to do, in response to a signal it received correctly. The mark is the record of an injury, not a defect.

Why it lands harder on darker skin

Melanocytes in richly pigmented skin are not more numerous. They are more responsive. Greater baseline melanin production and more reactive melanocytes mean the same inflammatory signal produces a larger pigment response.¹

The numbers follow. Among people with darker skin tones who have acne, the incidence of post-inflammatory hyperpigmentation runs as high as 65 percent.¹ It is particularly common in people of African, Asian and Latin American descent, and in that population the pigment left behind is frequently more distressing than the acne that caused it. Patients will tell you the breakout lasted a week. The mark has lasted a year.

Why depth decides the timeline

This is the part that determines what I can honestly promise, so it is worth understanding.

If the excess pigment stays in the epidermis, it looks brown, and it clears. Epidermal PIH typically resolves or substantially improves within six to twelve months, faster with treatment.¹ The epidermis renews itself, and the pigment leaves with it.

If inflammation is severe or prolonged enough to breach the junction between epidermis and dermis, melanin drops into the dermis, where roaming immune cells engulf it. That is called pigment incontinence, and the cells holding the pigment are melanophages. Dermal PIH looks different, more blue-gray than brown, and it behaves differently. It improves slowly and may be permanent.¹ The dermis does not turn over the way the epidermis does.

A Wood lamp helps distinguish the two in the room, which changes the conversation entirely.¹ One version is a waiting problem. The other is a management problem. A provider who tells you which one you have, before selling you a package, is doing the part that matters.

The first rule is to treat the inflammation, not the mark

This is where most PIH treatment goes wrong, and it goes wrong in an understandable way.

The pigment is what the patient can see, so the pigment is what gets treated. But if the acne is still active, or the eczema is still flaring, every new lesion is manufacturing new pigment behind you faster than you are clearing the old. You are bailing a boat without patching it.

So the sequence is not negotiable: bring the underlying inflammatory condition under control first.¹ This is also why several of the best agents for PIH are ones that treat both problems at once. Retinoids address acne and pigment simultaneously. So does azelaic acid.¹ When a single agent closes the tap and drains the sink, use it.

Sunscreen is the treatment, not the accessory

Ultraviolet exposure intensifies existing pigmentation and prolongs the time to resolution.¹ Every topical agent listed below is working against the sun, and the sun is patient.

I raise this early with patients rather than as a footnote, because daily photoprotection is doing more of the work than most people believe, and because a treatment plan without it will underperform in a way that looks like the treatment failing. Recurrence is common, and inadequate sun protection is the usual reason.¹

What actually works on the pigment

Treatment is stepwise and multimodal, and it takes months rather than weeks.¹

Hydroquinone remains the mainstay. It inhibits tyrosinase, the enzyme melanocytes need to manufacture melanin, and it has the longest track record of anything on this list. A widely used triple combination pairs hydroquinone 4 percent with tretinoin 0.05 percent and a low-potency corticosteroid, with the steroid deliberately limited to about eight weeks.¹

Retinoids such as tretinoin, adapalene and tazarotene accelerate epidermal turnover and treat acne at the same time, which makes them well suited to long-term use.¹ Azelaic acid does similar double duty and tends to be better tolerated.

Topical cysteamine is a more recent addition and among the more potent options now available for pigmentation disorders.¹ Tranexamic acid has accumulated meaningful evidence in both melasma and PIH, and is a useful option for patients who cannot tolerate hydroquinone or who need something for maintenance.²

None of these is dramatic on its own. Combined, applied consistently, and given the months they need, they work.

Where peels and lasers fit

Both can help. Both can also cause the exact problem you are treating, which is the tension that governs everything here.

Chemical peels using glycolic, salicylic or trichloroacetic acid remove epidermal cells carrying the excess pigment. In darker skin they demand a cautious hand, because a peel that irritates too aggressively produces new inflammation and therefore new pigment.¹

Lasers carry the same double edge. Q-switched and picosecond devices are used for pigment, and in deeper skin they require conservative parameters and an operator who understands why.¹ The wavelength and settings that make a laser safe in pigmented skin are the whole subject of a separate piece, and they matter here more than almost anywhere, because the patient in front of you has already demonstrated that her skin responds to injury by making pigment.

That is the clinical logic in one line. Somebody with a history of PIH has told you, in advance, exactly how her skin will answer an aggressive treatment.

What to expect

Improvement is slow, and recurrence is common without photoprotection.¹ Epidermal pigment usually clears over six to twelve months with consistent treatment. Dermal pigment improves gradually and may not fully resolve.

I would rather say that plainly at the first visit than have someone conclude at week six that nothing is working. This is a condition that rewards patience and consistency, and punishes aggression. Most of the damage I see was done by treatments that promised to be faster.