When at primary school, a poor lad had exczema on his hands and the initials of his name spelt Rad.For some reason when wither myself of siblings have a mild case of skin irritation, this is referred to as rad, or raddigans.
Rad coming from radical, (putting an emphasis on cool or awesome) the word was developed from skaters and surfers from late 70's -early 80's coming from California, Los Angeles. i.e see movies's from the early- mid 80's (Rad & Gleaming the Cube).