What is a halo naevus?
A halo naevus is a mole around which a pigment-free ring of skin has developed.
What does it look like?
With a halo naevus there is a round, white patch of skin visible with a mole in the centre. The colour of the mole varies from light brown to very dark brown. Sometimes the depigmented ring is very narrow, sometimes as much as a few centimetres wide. In people with a light skin type the halo can be very subtle.
How does it develop?
Although the precise cause is not entirely clear, there is probably an autoimmune process: the pigment cells around the mole are cleared away by the body’s immune system. This process strongly resembles what happens in the skin in vitiligo. The immune reaction is triggered, in a way that is not yet clarified, by factors in the mole that forms the core of the halo naevus.
Who gets it?
Halo naevi are not rare in children and young adults, and often several halo naevi are present at the same time. Adults can also develop them.
How is it treated?
Halo naevi are usually completely benign. However, just as with ordinary moles that change, the doctor will inspect every halo naevus critically. Usually halo naevi can safely be left in place. In case of doubt, the dermatologist will proceed to surgical removal, and the removed tissue is then sent to the pathologist for examination.
What is the outlook?
Usually, over time, all the pigment disappears from the mole, after which the normal pigmentation of the skin generally returns. Sometimes, however, the white patches persist for a very long time. Because the protective pigment has completely disappeared at these spots, extra care must be taken that they do not burn in the sun.
When to see a doctor
See your GP or a dermatologist to have a halo naevus checked, and promptly if the central mole is irregular, changing in colour, shape or size, itching or bleeding, so that anything suspicious can be assessed. Protect the depigmented ring from the sun, as it lacks its natural protection.