Congenital naevi or birthmarks are essentially coloured skin markings that develop before or shortly after birth. Naevi are sometimes called hamartomas, which are disordered proliferations of cells within the tissue of origin, and are due to developmental error.
Benign developmental skin lesions that develop later in life are called ‘acquired’ naevi.
Naevi may be derived from the outside layers of the skin (epithelialnaevi) or from the deeper layers (dermal/subcutaneousnaevi). Naevi are further classified based on the cell type involved. Melanocytic and vascularnaevi are generally the most common types of birthmarks.
Naevi are caused by visible clusters of cells in the skin. Vascularnaevi are due to clusters of blood vessels, melanocyticnaevi are due to clusters of pigmented skin cells (melanocytes), epidermalnaevi to keratinocyte skin cells and so on. The exact cause of why these occur is unknown but it may relate to localised abnormalities of certain genes. There is no known way to prevent them.
New ideas are being explored relating to mosaicism (the phenomenon of two cell lines arising early in embryonal development), as it has been observed that many congenital naevi follow the lines of Blaschko.
What treatment is available?
See individual birthmark types for specific treatment options.