Hi there. From your description, it does appear that you may have had a viral infection called herpes zoster
. The good news is if so, youmay almost never get it again & the worst is over. Dont pull off the scabs as healing will then be better with less scarring! I doubt it is a contact dermatitis
. Do keep an eye out & if it does spring up again, then i stand corrected & yes it could be some form of contact dermatitis or some infection like a cercarial dermatitis or other bacterial infection. For the moment, am pretty sure have nailed it & all will be well. Good luck & happy surfing..perhaps some day i shall take it up..sadly, Blore where i live has no sea :( Cheers!