Sebaceous naevus
Author: Blake Mumford


  • Alternate names: naevus sebaceous of Jadassohn, organoid naevus
  • Congenital hamartoma of skin comprised of:
    • Immature hair follicles
    • Epidermal hyperplasia
    • Sebaceous and apocrine glands
  • 0.3% of newborns; no sex predilection


  • Caused by post-zygotic somatic mutations in HRAS (95%) or KRAS (5%) genes
  • Mutations lead to activation of MAPK and PIK3-Akt pathways

Clinical manifestations

  • Usually apparent at birth, but subtle lesions may be missed until later in childhood
  • Well-circumscribed, yellow-orange, hairless plaque
  • Usually located on the scalp, face, neck; trunk is rarely affected
    • Scalp lesions are most common and cause alopecia
  • Linear lesions are distributed along lines of Blaschko
  • Grows proportionally with age
  • At puberty becomes thicker, with verrucous/nodular surface


  • Usually clinical
  • Histopathology can confirm the diagnosis


  • Acanthosis, papillomatosis
  • Presence of immature hair follicles is diagnostic
  • After puberty: abundant sebaceous glands
  • Apocrine glands usually present in specimens deep enough


  • Multiple types of neoplasms have been reported to arise within sebaceous naevus:
    • Trichoblastoma is the most common
    • Other tumours: tricholemmoma, syringocystadenoma pappiliferum
  • Malignant transformation is rare: basal cell carcinoma (< 1%)


  • Excision in late childhood is commonly utilised for facial lesions before verrucous surface changes emerge
  • Excision for the purpose of preventing future malignancy is debated
  • Observation is reasonable for lesions not situated in cosmetically sensitive areas