Hyperpigmentation: Causes, Safety & Honest Evidence

PIH is triggered by inflammation of any kind, which stimulates the pigment-producing cells to overproduce melanin. In darker skin specifically, the most common triggers are acne, atopic dermatitis (eczema) and impetigo. But the trigger list is wider than skin conditions alone; it also includes infections, allergic reactions, psoriasis, lichen planus, certain medications, thermal burns, and, importantly, cosmetic procedures themselves: laser therapy, chemical peels and cryotherapy are all recognised triggers of PIH, not just causes people arrive with. That last point matters, because it means the very treatments used to fade pigmentation can also cause it.

Solar lentigines are driven by chronic ultraviolet exposure over years, which causes changes that increase melanin production and retention within skin cells. Interestingly, the number of pigment-producing cells is normal or only slightly increased; it is more melanin per cell, not necessarily more cells. Several gene variants have been linked to solar lentigo formation, and fair Fitzpatrick skin types (I–II), a history of sunburn and sunbed use are the main risk factors, alongside cumulative age-related sun exposure.

A pigmented patch should not be assumed benign by appearance alone

The UK primary-care referral system for suspected skin cancer applies to any pigmented lesion, not only lesions that look like a classic mole. UK clinical guidance is direct that a suspicious pigmented lesion scoring three or more on the weighted seven-point checklist: a change in size, an irregular shape or border, and irregular colour scoring two points each; diameter of 7mm or more, inflammation, oozing or a change in sensation scoring one point each: should be referred on the two-week urgent suspected-cancer pathway.

In practical terms: a patch that is new, changing, asymmetric, irregularly coloured, or growing should be assessed by a clinician before being assumed to be PIH, a lentigo, or ordinary pigmentation. It should not be self-diagnosed from a description on a website.

This distinction matters because solar lentigines sit on a spectrum with more serious lesions. Melanoma in situ and lentigo maligna are listed in the differential diagnosis for solar lentigo, and require dermoscopy and biopsy to tell apart from a benign lentigo. Lentigo maligna specifically is a pre-cancerous condition, with approximately 5% converting to melanoma: a figure that rises to around 50% in lesions larger than 4cm. Some lesions that look like an ordinary “age spot” to a patient are a genuinely different, higher-risk entity that needs proper clinical assessment, not patient self-assessment.

The treatment itself can cause the problem it is meant to fix

This is the single most important point for a cosmetic clinic to state plainly, and we would rather you know it before booking than after. A systematic review of 46 studies covering 1,356 participants with skin of colour states it directly: “Treating PIH poses challenges and can potentially worsen the condition.” On chemical peels specifically, the same review found people with skin of colour have “a well-documented elevated risk of developing PIH transiently after peels compared to the general population.”

On laser treatment: “Laser poses an increased rate of inducing PIH with repeated procedures (11%-17%), especially in darker skin types”, even though laser also produced the review’s best complete-resolution rate (26% of a subgroup), it also produced documented cases of PIH getting worse after treatment. The practical implication: pigmentation treatment plans need to be conservative and patch-tested in darker skin types, and you should be told plainly that treatment carries a real risk of worsening pigmentation, not only a chance of it not working.