Post-inflammatory hyperpigmentation: causes, treatment and how long it takes to fade

PCDS describes post-inflammatory hyperpigmentation (PIH) as darkening of the skin that occurs after an inflammatory eruption, such as acne, eczema or lupus, or following injury to the skin. There may be a history of itch or signs of active skin disease, such as redness and scale. On occasions the skin can instead become lighter, called hypopigmentation.

It is not dangerous, but it can cause distress. PCDS notes that facial hyperpigmentation is common and can have a significant emotional impact.

PCDS explains that all people have roughly the same number of melanocytes (pigment-making cells) in the skin, regardless of colour. What differs is the size and distribution of the melanosomes, the structures that carry melanin. Higher levels of melanin and larger melanosomes give greater protection from the sun, but they also correlate with more post-inflammatory hyperpigmentation after inflammation and trauma.

Skin of colour in this context means Fitzpatrick skin types IV to VI. PCDS says acne is no more common or severe in skin of colour, but the PIH it leaves can be significant and often persists for months to years. It therefore advocates early and more active acne treatment.

Anything that inflames or injures the skin can leave pigment behind. PCDS lists acne, eczema, lupus and skin injury. The British Association of Dermatologists says acne can leave scars or marks on the skin, particularly where there are nodules and cysts, and can leave discolouration that may be red, darker than your usual skin colour (hyperpigmented) or lighter (hypopigmented). The NHS advises not picking or squeezing spots because this can cause scars.

PCDS also lists other things that can cause patches of dark skin, which your doctor will consider because they need different treatment.

PCDS says the time taken for affected skin to lighten is highly variable and can take several years. Epidermal PIH, where the pigment is in the top layer of the skin, will take 6 to 12 months to fade. Deeper pigment may take years. A Wood's light (a special ultraviolet lamp) can help show how deep the pigment is, because it enhances the colour if the pigment is mainly epidermal.

PCDS says the main aim of treatment is to treat any ongoing inflammation. The condition that caused the pigmentation needs to be controlled, otherwise new marks keep forming.

• Treat the cause promptly and effectively, for example acne or eczema. See a GP or pharmacist if over-the-counter treatment is not working; the NHS advises seeing a GP if acne is causing scars or affecting mental health.

• Use a sunscreen with a minimum SPF of 30 every day, to stop the marks darkening.

• Be careful with acne treatments such as topical retinoids, benzoyl peroxide and azelaic acid. PCDS says daily use often causes dryness and irritation, which in skin of colour can lead to further hyperpigmentation, so they should initially be used for shorter periods and perhaps less frequently, with duration and frequency increased if tolerated.

• Avoid self-applied chemical bleaching creams. PCDS says hydroquinone or resorcinol, used without advice, can cause exogenous ochronosis.

• Phototherapy has been used successfully in some people, according to PCDS.

• Camouflage can help. PCDS says people can be referred to camouflage clinics, which can advise on the best ways of covering up affected areas, and the British Association of Dermatologists describes skin camouflage as an inexpensive and effective method of disguising pigment changes.

See a GP if dark patches are spreading, itchy, painful or changing, if they are not clearly related to a previous skin problem, or if they come with symptoms such as tiredness, weight loss or dizziness, because PCDS lists Addison's disease and haemochromatosis among the serious causes of pigmentation that must not be missed. See a GP too if you have used a lightening cream and the skin has turned blue-black, as this may be exogenous ochronosis.

For acne, the NHS advises seeing a GP if you have tried treating it yourself but it is not getting better, if there are lots of spots or they are deep, painful or causing scars, or if it is affecting your mental health.

On the NHS, your GP can assess the pigmentation, treat the underlying skin condition and refer you to a dermatologist if needed. PCDS says patients can be referred to camouflage clinics, which may be found in local outpatient departments. Some people choose a private dermatologist for assessment of pigmentation. PCDS describes the evidence for laser treatment in some pigmentary conditions as limited, so it is reasonable to ask what evidence supports a suggested treatment before paying for it.