Nah, no spidery kind of thing. My guess is a reaction to the hat itself, or a reaction to something in the hat (detergent. moth balls, etc).

Seriously.......have you ever had a bad sunburn or a bad flu reaction in that area of your head/scalp? If yes, you may have a "weakness" in that area that makes you susceptible to reactions in that area.

I have that exact issue with the inner part of my left shin/calf area.