It could be a variety of things, but definitely sounds like contact dermatitis. Allergies come and go, meaning that, what you were not allergic to previously might spontaneously show up on you. I'm pretty sure a doctor will tell you that it's the change of detergent or other cosmetic products. That's likely, but not always the case. From your explanation, it doesn't sound harmful. If your in a hot and humid environment, it could also ...