Hi...Tom Wrensen..,
Thanks for choosing HCM.,
 
HAIRY NEVUS.....   Usually brown to dark brown in pigmentation
    Large surface area may involve 
scalp, face, trunk, or extremity
    May develop nodules which warrant biopsy
    Risk of 
melanoma transformation is 10-15%, and can occur in childhood
    Treatment ranges from conservative observation with biopsy of suspicious areas to staged excision, often involving the use of skin balloon expanders or skin grafts...or 
LASER therapy
    So don't worry...Transformation to cance is very less chance...,
     But observe always the following.....A--B--C--D--E---
    1) A-- Asymmetry...uneven.,
2)B-- Border of nevi ...irregular with poorly defined border.,
3)C-- Color...different shades from Brown to Black..,
4)D-- Diameter...mor than 6 mm in size..(Rubber eraser size).,
5)E-- Evolving....changes with growing...,
So keep in mind and aviod problematic HAIRY NEVI....ok good luck