Dr Bernadette Carr is here to answer your questions

My sister developed white patches on her skin recently and has been diagnosed with vitiligo. I have never heard of this, could you explain what it is?

Vitiligo is a condition that causes flat white patches to develop on the skin due to a lack of the pigment melanin. It affects around 1% of the world’s population, with both men and women equally affected. The onset usually occurs before 20 years of age in 50% of patients. It is common and tends to appear on the parts of the skin that are exposed to the sun — face, neck, and hands. Patches of the white skin can appear on the same places on both arms or both legs.

The skin consists of two layers, the epidermis (upper) and the dermis (lower) and in the dermis there are cells called melanocytes which produce melanin which colours the skin and helps to protect it from the rays of the sun. It is melanin which causes the skin of fair skinned people to tan.