↑ James, William; Berger, Timothy; Elston, Dirk (2005) Andrews' Diseases of the Skin: Clinical Dermatology (10th ed.). Saunders. Page 17. ISBN 0721629210.
↑ No absolute size, or range of sizes, is specified in this definition, as there seems to be no general consensus within the literature, reflected in the text Andrews' Diseases of the Skin: Clinical Dermatology (see references), a work considered by some dermatologists as an authority on this subject matter, in which no size is specified.