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DermNet NZ


Facts about the skin from DermNet New Zealand Trust. Topic index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z



Naevi (birthmarks)

What are naevi?

Congenital naevi or birthmarks are essentially coloured skin markings that develop before or shortly after birth. Benign developmental skin lesions that develop later in life are called ‘acquired’ naevi.

Naevi may be derived from the outside layers of the skin (epithelial naevi) or from the deeper layers (dermal/subcutaneous naevi). Naevi are further classified based on the cell type involved. Melanocytic and vascular naevi are generally the most common types of birthmarks.

Epithelial naevi Dermal/subcutaneous naevi
Melanocytic naevi
Vascular naevi
Epidermal naevi
Connective tissue naevi
  • Collagenoma
  • Elastomas
  • Elastosis perforans serpiginosa
  • Congenital smooth muscle hamartoma
  • Fat naevus (naevus lipomatosis)
    • Michelin tyre baby
  • Congenital fibromatosis
  • Mucinous naevus
Follicular naevi
Other developmental defects

What causes naevi?

Naevi are caused by visible clusters of cells in the skin. Vascular naevi are due to clusters of blood vessels, melanocytic naevi are due to clusters of pigmented skin cells (melanocytes), epidermal naevi 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.

Related information

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Author: Vanessa Ngan, staff writer

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If you have any concerns with your skin or its treatment, see a dermatologist for advice.