Author: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, 2004.
Idiopathic guttate hypomelanosis is the name given to 2 to 5-mm flat white spots found on the shins and forearms. ‘Idiopathic’ means the cause is unknown, ‘guttate’ means resembling tear-drops, and ‘hypomelanosis’ refers to the lighter colour of the affected areas.
Idiopathic guttate hypomelanosis predominantly affects fair-skinned individuals, but it may occasionally arise in darker skin. Although most often found on the shins and sun-exposed parts of the forearms, guttate hypomelanosis may also arise on other sun-exposed areas including the face, neck and shoulders. The white marks are usually smooth with a reduction in the normal skin markings, but they may be slightly scaly.
They appear as part of the ageing process, becoming quite common in those over 40 years of age. They are more common in women than in men. Inherited factors may be relevant as the lesions appear to be more common in family members.
A skin biopsy demonstrates that there is no pigment (melanin) in the skin cells (keratinocytes). There is also a reduction in the number of pigment-producing cells (melanocytes). The skin is slightly thinner than normal and flattened out.
The cause of guttate hypomelanosis is speculative. It is thought to be an inevitable part of the ageing process, with a gradual reduction in melanocytes – a similar process to greying of hair. Other theories include:
Idiopathic guttate hypomelanosis does not appear to be due to trauma or viral infection. The white areas do not predispose to skin cancer.
In most cases, treatment is not required as the marks are completely harmless. Attempts to destroy the lesions may leave brown marks or larger white marks, which may look worse than the original condition. Sun protection is very important.
The following measures may improve the appearance.
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