Why Does Hyperpigmentation Happen?

Hyperpigmentation has a wide range of causes, and in many cases, more than one factor is involved. Broadly, triggers fall into a few main categories: sun exposure, inflammation, hormonal changes, medications, and, in rare cases, underlying health conditions.

Sun exposure

UV radiation is one of the most common drivers of hyperpigmentation. When the skin is exposed to sunlight, melanocytes produce more melanin as a protective response. Over time - particularly with repeated, unprotected exposure - this leads to the uneven patches commonly known as sun spots, age spots, or solar lentigines. These tend to appear on areas that receive the most sun: the face, neck, hands, and forearms.

Inflammation and skin injury

When the skin experiences inflammation - from acne, eczema, a cut, a burn, or any kind of trauma - the healing process can trigger melanocyte activity in the affected area. The resulting dark marks are known as post-inflammatory hyperpigmentation (PIH). This is one of the most common types, and it can follow even a relatively minor skin disruption.

Hormonal changes

Shifts in hormone levels - particularly oestrogen and progesterone - can directly stimulate melanin production. This is the most common mechanism behind melasma, the type of hyperpigmentation that often develops during pregnancy, while taking the combined oral contraceptive pill, or during perimenopause. Hormonal hyperpigmentation is covered in more detail in the next section.

Medication

Several medications can trigger or worsen hyperpigmentation as a side effect. These include certain antimalarial drugs, some antibiotics, tricyclic antidepressants, and chemotherapy agents. Some topical products - particularly those containing irritating ingredients used incorrectly - can also cause localised darkening.

Can my medication be causing it?

If pigmentation has developed or worsened since starting a new medication, it is worth raising with a GP or pharmacist. The relationship between medication and skin colour change is not always well publicised, and it is an easy factor to overlook.

When is pigmentation a sign of something more serious?

In most cases, hyperpigmentation is a cosmetic concern with no underlying health implications. That said, two conditions are worth knowing about.

Addison's disease - a condition affecting the adrenal glands - can cause widespread skin darkening, particularly in skin creases, on scars, and inside the mouth. Haemochromatosis, an inherited condition involving iron overload, can give the skin a bronze or grey-brown appearance. Both are rare, but both warrant medical investigation if other symptoms are present. These are covered in more detail in the section on when to see a doctor.

Hormones play a more significant role in hyperpigmentation than many people realise - and the connection goes well beyond pregnancy. Several hormonal pathways can influence melanocyte activity, which helps explain why pigmentation sometimes appears or worsens at life stages or during periods seemingly unrelated to sun exposure or skin damage.

Oestrogen, progesterone, and melasma

The most well-documented hormonal trigger is the relationship between oestrogen and progesterone and a type of hyperpigmentation called melasma. These hormones can stimulate melanocytes directly, encouraging excess melanin production - particularly in sun-exposed areas of the face such as the cheeks, forehead, and upper lip.

Melasma is significantly more common in women, and it frequently develops during pregnancy, when taking the combined oral contraceptive pill, or during perimenopause - all points at which oestrogen and progesterone levels shift. It can also occur in people taking hormone replacement therapy (HRT). That said, not everyone who experiences these hormonal changes will develop melasma. Genetics, sun exposure, and skin type all influence whether the condition appears and how pronounced it becomes.

The contraceptive pill and HRT

It is worth being specific here, because this is something many people are uncertain about. The combined pill - which contains both oestrogen and progesterone - carries a higher association with melasma than the progesterone-only pill. If pigmentation has developed or worsened since starting hormonal contraception, it is reasonable to raise this with a GP, as alternatives may be worth considering.

HRT carries a similar but less extensively studied association. Given that perimenopause itself can trigger hormonal pigmentation, this can make the picture harder to unpick - and it is another reason why a clinical assessment is useful rather than assuming sun damage is the sole cause.

Does stress really affect skin pigmentation?

This is an angle that rarely appears in consumer-facing content, but the evidence behind it is genuine.

Chronic stress triggers the release of a hormone called adrenocorticotropic hormone (ACTH) from the pituitary gland. ACTH is part of the same hormonal pathway that regulates melanin production - specifically, it stimulates the production of alpha-melanocyte-stimulating hormone (alpha-MSH), which directly activates melanocytes. In other words, sustained psychological stress can, over time, contribute to increased pigment production through a measurable hormonal mechanism.

Separately, stress-driven inflammation can also trigger post-inflammatory hyperpigmentation even without an obvious skin injury. The two pathways - hormonal and inflammatory - can compound one another.

This does not mean that stress alone will cause visible dark patches overnight. But for people who notice pigmentation worsening during particularly pressured periods, there is a plausible biological explanation - not just a coincidence.

For people with deeper skin tones, hyperpigmentation is not just more common - it can be more intense, more persistent, and more difficult to treat. This is not a matter of perception. There are clear biological reasons why the same trigger that leaves little trace on fair skin can produce months or years of visible darkening in someone with a deeper complexion.

The biology behind the difference

Skin tone is determined by the activity of melanocytes, not their number. People with Fitzpatrick skin types III to VI - a clinical scale used to classify skin from very fair to very deep - have melanocytes that are more reactive and produce melanin more readily in response to any form of stimulation. When inflammation, injury, or a hormonal trigger occurs, the melanocyte response in deeper skin tones tends to be stronger and more sustained.

Research published in StatPearls notes that the incidence of post-inflammatory hyperpigmentation in darker-skinned individuals with acne can be as high as 65%. That is a significant figure - and it helps explain why PIH following acne is one of the most common reasons people with skin of colour seek dermatological care in the UK.

Why do some dark marks last for years while others fade in weeks?

Two factors determine this: the depth of the pigment and the skin type of the person affected.

As discussed earlier in this article, epidermal pigmentation is closer to the surface and is more likely to fade over time as the skin renews. Dermal pigmentation - where melanin has migrated deeper - is considerably more resistant. In deeper skin tones, dermal involvement is more likely, in part because more reactive melanocytes produce larger volumes of melanin that the skin's upper layers cannot fully contain.

There is also the matter of what triggered the pigmentation in the first place. Deeper or more prolonged inflammation tends to drive melanin deeper into the dermis. For someone managing a long-standing inflammatory condition such as eczema or cystic acne - both of which disproportionately affect people with skin of colour - the cumulative effect on pigmentation can be considerable.

A gap in UK clinical care

This is worth stating plainly. Research into hyperpigmentation treatments has historically been conducted predominantly on lighter skin types, meaning the evidence base for managing PIH in skin of colour is thinner than it should be. A 2022 paper in Clinical and Experimental Dermatology noted limited training in ethnic dermatology in UK clinical settings, despite a growing population of people with skin of colour. A 2025 piece in the Pharmaceutical Journal highlighted that delayed diagnosis in darker skin tones leads to prolonged inflammation, which, in turn, worsens hyperpigmentation.

The practical implication is that people with deeper skin tones may need to be more proactive in seeking assessment from a practitioner with specific experience in skin of colour. Not all treatments appropriate for lighter skin are safe or effective across all skin types - a point covered in the next section.

It is a question that does not get asked often enough before treatment - and one that can cause significant distress when the answer turns out to be yes. Certain aesthetic and dermatological procedures can trigger hyperpigmentation as a direct consequence of their mechanism of action, rather than as a sign that something has gone wrong.

Which treatments carry a risk?

Any procedure that causes controlled injury or inflammation to the skin carries a potential risk of post-inflammatory hyperpigmentation. This includes:

• Laser and light-based treatments - including resurfacing lasers, IPL (intense pulsed light), and some pigmentation-targeting devices
• Chemical peels - particularly medium and deep peels that penetrate beyond the superficial skin layer
• Microneedling - which creates micro-injuries to stimulate collagen production
• Cryotherapy - the use of extreme cold to treat localised skin lesions
• Dermabrasion - mechanical exfoliation at a clinical depth

This is not a list of treatments to avoid. Many of these procedures are effective, evidence-based options for a range of skin concerns. The point is that they all involve a degree of skin trauma, and in some individuals - particularly those with deeper skin tones - that trauma can stimulate excess melanin production in the treated area.

Why is the risk higher in deeper skin tones?

As covered in the previous section, people with Fitzpatrick skin types III to VI have more reactive melanocytes. A laser wavelength or peel depth that produces minimal pigmentation response in a fair-skinned patient can cause significant and persistent PIH in someone with a deeper complexion. This is not a rare complication - it is a predictable biological response when treatment parameters are not adjusted appropriately for skin type.

Importantly, this risk can be substantially reduced with the right assessment and approach. Patch testing, appropriate device selection, adjusted energy settings, and thorough pre-treatment preparation all matter. In practice, it means that the practitioner's experience and skin-type expertise are at least as important as the treatment itself.

What about topical products?

Some skincare ingredients can also cause or worsen hyperpigmentation if used incorrectly. Certain acids used at too high a concentration, products that cause irritation or allergic contact dermatitis, and - counterintuitively - some brightening ingredients used without adequate sun protection can all contribute to pigmentation changes. Riehl melanosis, a form of contact pigmentation, is a specific example noted in UK clinical guidance, caused by photocontact allergic reactions to certain ingredients.

If a new product or treatment coincides with the onset of pigmentation, that timing is worth noting and raising with a practitioner.

Whether hyperpigmentation fades on its own depends on several factors: the type and depth of the pigment, the original trigger, and the individual's skin type. For some people, marks improve noticeably within a few months once the cause is addressed. For others, they persist for years or do not fully resolve without intervention. Honest expectation-setting here matters because many people wait longer than necessary before seeking advice.

Epidermal hyperpigmentation

Epidermal pigmentation, located in the upper layers of the skin, has a reasonable chance of fading over time. As the skin naturally sheds and renews, excess melanin in the epidermis gradually moves toward the surface and is shed with dead skin cells. This process can take anywhere from a few months to well over a year, and it is significantly influenced by two things: whether the original trigger has been resolved, and whether consistent sun protection is in place.

Sun exposure is worth emphasising here. UV light actively stimulates melanocyte activity, meaning that even incidental sun exposure - a daily commute, sitting near a window - can slow or reverse the fading process. Epidermal hyperpigmentation that might otherwise improve can persist indefinitely if sun protection is not a consistent part of daily routine.

Dermal hyperpigmentation

Dermal pigmentation is considerably less likely to resolve on its own. Because the melanin has been taken up by macrophages deep in the dermis, it is beyond the reach of the skin's natural renewal process and largely inaccessible to most topical treatments. In some cases, it does fade slowly over a long period. In others, it is effectively permanent without clinical intervention.

The blue-grey appearance associated with dermal hyperpigmentation can sometimes be mistaken for bruising or vascular changes - another reason why a proper assessment is useful if pigmentation does not behave as expected.

Skin type and fading timelines

Skin type plays a direct role in how quickly - or whether - hyperpigmentation fades. As discussed in the earlier section on darker skin tones, people with Fitzpatrick types III to VI tend to experience more sustained pigmentation responses. The fading process, even for epidermal marks, can take considerably longer than in fairer skin. In some cases, marks that would resolve within weeks in lighter skin persist for a year or more.

That said, fading is not impossible, and timeline should not be mistaken for permanence. Managing the original trigger, protecting the skin consistently from UV, and - where appropriate - seeking clinical advice can all make a meaningful difference.

Most hyperpigmentation is a cosmetic concern rather than a medical one, and in many cases, it does not require clinical input to manage. That said, there are situations where getting a professional assessment is genuinely important - and a few where it is urgent.

Signs that warrant a GP appointment

The following are worth raising with a GP, particularly if they are new or unexplained:

• Pigmentation that has appeared suddenly or spread quickly across a wide area
• Darkening that is not confined to sun-exposed areas, or that affects skin folds, the gums, or the inside of the mouth
• Pigmentation accompanied by other symptoms - persistent fatigue, unexplained weight loss, dizziness, or digestive changes
• Skin that has darkened significantly without an obvious trigger, such as sun exposure, inflammation, or medication
• A mark that has changed in colour, shape, or size over a period of weeks

The first three points in particular may indicate an underlying systemic condition. As noted earlier in this article, Addison's disease and haemochromatosis are both associated with generalised skin darkening and require medical investigation. Neither is common, but both are conditions that should not be missed - and both are manageable when identified and treated appropriately.

When to seek a dermatologist or specialist

Beyond GP-level concerns, there are also situations where a dermatologist or aesthetics practitioner with skin pigmentation expertise is the more appropriate route:

• Hyperpigmentation that has not improved after several months of consistent sun protection and basic skincare
• Pigmentation in deeper skin tones where previous treatment has had a limited effect or caused worsening
• Melasma that is recurrent, widespread, or has not responded to standard topical approaches
• Any uncertainty about which type of hyperpigmentation is present, particularly where clinical assessment tools such as Wood lamp examination may be helpful

In the UK, referral to NHS dermatology for cosmetic pigmentation concerns is generally not available through standard GP pathways. Private dermatology appointments and aesthetic clinics with specialised expertise in skin pigmentation are typically the practical route for those seeking a more in-depth assessment or treatment.

A specific note on the skin colour

It is worth repeating a point made earlier. Research has shown that skin conditions in people with darker skin tones are more likely to be missed or misidentified in primary care settings. If a GP assessment does not feel adequate - or if a diagnosis does not fit the pattern of what is being experienced - seeking a second opinion from a practitioner with specific experience in skin of colour is a reasonable and legitimate step.