Skin pigmentation disorders affect the colour of the skin. Skin gets its colour from a pigment called melanin. Special cells in the skin called melanocytes make melanin. When the melanocytes are hyperactive or make too much melanin it will lead to hyperpigmentation or darkening of the skin, and when melanocytes are underactive or make too little it will lead to hypopigmentation or whitening of the skin. Some pigmentation disorders can affect the entire skin, whilst others affect the skin in patches.
Hyperpigmentation
Medical conditions that increase the hormone that stimulates melanocytes to produce melanin may lead to generalised hyperpigmentation. This includes conditions like Addison’s disease. Generalised hyperpigmentation is not very common.
Localised hyperpigmentation is very common. Some of the common causes include post-inflammatory hyperpigmentation from previous injury, prior or current acne, following eczema, or following a fixed drug reaction (a form of allergy to medications). This condition is much more common in dark-skinned patients.
Other common causes of localised hyperpigmentation include melasma — a hormonally-influenced pigmentation disorder more common in females, and lichen planus pigmentosus — also mainly affecting females especially in the sun-exposed areas. Freckles, moles, acanthosis nigricans, and dermatosis papulosa nigra are also very common.
Worrying pigmented lesions on the skin can be skin cancers — if a new suspicious pigmented lesion with irregular borders and colour appears, or an old mole suddenly changes, it needs to be checked by a dermatologist to rule out skin cancers. Common pigmented skin cancers include basal cell carcinoma and melanoma.
Hypopigmentation
Generalised hypopigmentation is found commonly in patients with albinism. It can also be a result of severe generalised vitiligo — a condition in which melanocytes stop producing melanin.
Localised hypopigmentation is more common than generalised hypopigmentation. Common conditions resulting in hypopigmentation are vitiligo, post-inflammatory hypopigmentation, pityriasis alba, and idiopathic guttate hypomelanosis.
For the treatment of any of the pigmentation disorders, it’s best to see a dermatologist.