The spot clears in a week. The brown mark it leaves behind can still be there six months later. That mark is post-inflammatory hyperpigmentation, and it is one of the most common reasons people book a skin consultation, often believing they have been left with a scar.
They usually have not. Understanding the difference decides everything about what to do next, because the treatments that improve a scar and the treatments that improve a mark are not the same.
What is post-inflammatory hyperpigmentation?
It is a flat patch of darker skin left behind after inflammation has settled. When the skin is inflamed, whether by a spot, a burn, a rash, a cut or a cosmetic treatment, the pigment-producing cells can respond by producing extra melanin in that spot. The inflammation resolves. The pigment stays.
The colour ranges from light brown to grey or almost black depending on your skin tone and how deep the pigment sits. The important feature is that it is flat. Run a finger across it and the skin feels level, unlike a scar, which changes the texture of the surface.
How is it different from the red marks?
Red or purple marks left after a spot are a different process, usually described as post-inflammatory erythema, and they are blood vessel changes rather than pigment. They tend to be more visible on lighter skin, while brown pigment marks are more common in medium and darker skin tones.
The distinction matters practically. Treatments aimed at pigment do very little for redness, and treatments aimed at redness do very little for pigment. Getting it wrong means a course of the wrong thing.
Why do some people get it and others do not?
Largely because of how readily your skin produces pigment in response to inflammation, which is determined by skin type. People with medium to deeper skin tones are more prone to post-inflammatory hyperpigmentation, and it tends to be darker and to last longer when it appears.
Beyond skin type, the main factors are how severe and how prolonged the inflammation was, and what happened afterwards. Two things reliably make it worse:
- Picking or squeezing, which extends the inflammation and deepens the mark
- Sun exposure without protection, which stimulates further pigment production in an area already primed to produce it
This is why the advice to leave spots alone is not cosmetic fussiness. The mark left by a spot that was picked is usually darker and slower to fade than the one left by a spot that was not.
Will it fade on its own?
Often, yes, but slowly, and how slowly depends on how deep the pigment sits. Pigment held in the upper layers of the skin usually fades over months as the skin renews itself. Pigment that has dropped deeper takes considerably longer and may not clear completely without treatment.
Two things change the timeline more than anything else. Daily sun protection, which prevents the mark being re-stimulated, and getting the original condition under control, because new inflammation simply produces new marks. Treating pigmentation while active acne continues is treating a moving target.
Which treatments actually work on it?
The useful question is where the pigment sits and how your skin responds to being treated, not which device is strongest. Aggressive treatment of pigmentation in skin that is prone to pigmenting can make the problem worse rather than better, which is the single most important point in this whole subject.
Topical and prescription routes
Many cases are managed first with topical treatment, and some need prescription-strength preparations that are only appropriate after medical assessment. Those are prescribed by a doctor when they are suitable for your skin and your situation, which is a conversation at consultation rather than something to choose from a website.
Light and laser treatments
Where a device is appropriate, the choice follows the depth of the pigment and your skin type.
- LaseMD is a gentler resurfacing approach often used where pigment sits in the upper layers and where a lower-risk profile is preferred
- Picosecond lasers such as PicoSure and PicoWay deliver very short pulses that break pigment mechanically rather than through heat, which matters in skin that reacts badly to heat
- IPL can be effective on sun-related pigmentation in lighter skin types but is generally not the route for post-inflammatory pigmentation in deeper skin tones
A patch test is carried out before any of these, and it is doing real work here rather than being a formality. It shows how your skin responds to a given setting before that setting is used across a visible area.
Why is treating pigmentation in darker skin different?
Because the same pigment response that produced the mark can be triggered again by the treatment. Melanin absorbs laser light, so in richer skin tones more of the energy is taken up by the surrounding skin rather than only the target, which raises the risk of both further darkening and, less commonly, patches of lighter skin.
The practical answer is conservative settings, appropriate wavelength choice and a slower course rather than a shorter one. A clinic that treats every skin type with the same protocol is not the right clinic for this particular problem.
What can you do while it fades?
- Wear a high-factor broad-spectrum sunscreen daily, including in winter and indoors near windows
- Leave spots alone, however tempting
- Get the underlying acne or skin condition treated, rather than only the marks it leaves
- Give any treatment plan time, since pigment responds over months rather than weeks
- Avoid strong at-home acids or unregulated skin-lightening products, which can worsen pigmentation and carry their own risks
Does it come back?
The mark itself does not return once it has cleared. What returns is the process that caused it, so if the underlying acne, eczema or reaction is still active, new marks will keep appearing in new places while the old ones are being treated.
This is the reason a good plan treats both at once rather than in sequence, and the reason the first consultation asks a lot of questions about what is actually happening to your skin rather than only about the marks you want gone.
How long does a course take?
Longer than most people hope. Pigment sitting in the upper layers may shift over a few sessions across two or three months. Pigment that has dropped deeper can take six months or more, and some of it may not clear entirely.
Sessions are spaced by several weeks, partly to let the skin recover and partly because progress is genuinely difficult to judge week to week. Photographs taken in the same light at the same distance are worth more than memory here, and any clinic treating pigmentation properly will be taking them.
One thing that changes the timeline more than any device: what you do about sun exposure between appointments. Treating pigmentation while going out unprotected is spending money to undo work you are also paying for.
When is it worth having it looked at?
If the marks have not changed over several months, if new ones keep appearing because the underlying condition is still active, or if you are not sure whether you are looking at pigment, redness or genuine scarring. That last one is the most common reason people end up treating the wrong thing.
Pulse Light Clinic is CQC-registered and doctor-and-nurse-led, and has been treating skin in London since 2001. A consultation covers what is actually causing the marks, whether treatment is appropriate for your skin type, and what a realistic course looks like.
Book a consultation to have your skin assessed before starting any treatment for pigmentation.
