Why does hyperpigmentation occur?

What triggers the extra pigment?

Sunlight stimulates melanocytes to produce more melanin. Uneven production can create freckles, and a tendency to freckle runs in families. Repeated sun exposure also causes solar lentigines, commonly called sun spots or age spots, especially on the face and backs of the hands. Sunlight can darken marks that developed for other reasons, too.35

Inflammation from acne, eczema, burns or other injuries can stimulate extra melanin production. The pigment remains where the inflammation occurred after the skin has healed. This is called postinflammatory hyperpigmentation. If deeper skin layers are injured, pigment can also become trapped below the surface. Anyone can develop these marks, but they tend to be more intense and last longer in darker skin tones.5

Skin care and hair care products can trigger dark spots if they irritate the skin. Picking pimples or injuring the same area again can keep the problem going. Finding the cause comes before choosing a fading product, even if the bottle would prefer top billing.6

Hormonal changes during pregnancy and hormonal contraceptive use can trigger melasma, which produces brown facial patches, often on both sides. Melanocytes are more active in melasma, but exactly why is not fully understood. Sunlight is a trigger, and family history and medium to dark skin tones increase the risk. Some medicines and thyroid disease are also linked to melasma.17

Not all darkening comes from excess melanin. Some medicines, metals and excess iron can deposit other colored substances in the skin. Widespread darkening can also occur with conditions such as Addison disease or primary biliary cholangitis, a liver disorder. Dark, thickened skin around the neck or underarms can be acanthosis nigricans, which is sometimes associated with diabetes or PCOS.13

What should you do about it?

Addressing the trigger helps prevent new marks while existing ones fade. Sunscreen belongs in a pigmentation routine, even when a brightening serum has given itself the starring role.6

1. 1Identify the likely trigger. Consider whether the marks followed a breakout, rash, injury, new product or medicine. Treating an ongoing inflammatory skin condition comes before trying to fade its marks.
2. 2Remove avoidable irritation. Stop using a skin care product that burns or stings, choose gentler products and avoid picking. If a medicine seems responsible, ask the prescriber about alternatives rather than stopping it yourself.
3. 3Protect exposed skin daily. Use broad spectrum sunscreen with SPF 30 or higher, preferably tinted with iron oxide for visible light protection. Apply it before going outdoors and reapply every two hours outdoors and after swimming or sweating. Wear a hat and protective clothing.

How long does the pigment stay?

After the trigger stops, a spot a few shades darker than your usual skin color often fades within 6 to 12 months. Deeper pigment can take years. Melasma sometimes clears after childbirth or removal of a trigger, but it can persist for years. Peels and lasers can worsen postinflammatory pigmentation by causing further injury, so stronger treatment is not automatically the right treatment.567

When should a doctor check it?

Arrange an assessment for unexplained widespread darkening or dark, thickened folds. Ordinary hyperpigmentation does not cause pain or itching: seek medical care if the area is red, hot, itchy, painful, bleeding or leaking fluid. A clinician can review your medicines and examine the pattern, with blood tests when an underlying cause is suspected.12