Indeed, Mimi is probably right! Additionally, it may be caused more by a food allergy/intolerance, than by biking. I used to have similar smaller "blemishes" in the area very often. Since the restricted diet and general work to get healthier, I almost never do now! I also used a product call JAson Tea Tree Gel (contains aloe, tea tree, arnica, witch hazel and roman chamomile I think), which did wonders, too. And I always always always change out of my bike shorts as soon after a ride as possible.....

Maybe one of these things can help you?

Doesn't hurt to see a doc, too!

Hugs and big happy butterflies,
~T~