What is a birthmark? How does it form?

A: A birthmark is a coloured mark on the skin that is either present at birth or develops shortly afterwards. Most are completely harmless and painless. While some of them may fade over time, others stay for life.

Birthmarks are essentially ‘mistakes’ in the development of skin cells or blood vessels. They generally fall in one of two categories. Vascular birthmarks occur when blood vessels in a particular area do not form correctly, i.e. because there are too many of them or they may be wider than usual. The extra blood flow that results gives the skin there a red, pink or even purple appearance. Common examples include the so-called ‘stork bikes on the neck or the ‘strawberry’ marks.

Second, pigmented birthmarks are caused when melanocytes, the cells that give your skin its colour, overgrow in an area. As these cells cluster together, they create a patch that is darker than the surrounding skin. Common variations include moles, light-brown ‘café-au-lait’ spots, and bluish-gray patches. The exact reason why these clusters form is not known.

Birthmarks are also not caused by anything a mother does during pregnancy. They are random.

Have a question you’d like answered? Send an email to science@thehindu.co.in with ‘Question Corner’ as the subject.