The woolly border seen on dermoscopy of blue naevi is due to the presence of deeply pigmented spindle melanocytes blending with the surrounding skin within the dermis.
An 18-year-old man noticed a dark mole on his upper back (Figure 1), six months prior to consultation. He felt that the intensely pigmented mole (measuring 5 mm in diameter) had grown slowly in the interval. Dermoscopy revealed a symmetrical mole which had a homogeneous, structureless blue–black component in its centre, surrounded by a woolly border. The latter consisted of fine trails of blue–black pigment that were partially obscured by a light veil (Figure 2). Excision biopsy revealed a dermal infiltrate of deeply pigmented spindle-shaped melanocytes, which extended into the surrounding dermis but lacked nuclear atypia or mitoses (Figure 3).