Any number of things can cause cause chaffing or a rash to occur. Overuse can clog and block pores and sweat glands too, causing underarm problems such as rash, cysts and sores, burned skin, etc.
Your deodorant? I do that with like 90% of deodorant. Even if I've been using a certain kind for months, I'll still suddenly develop an allergic reaction to it at any time.
If it's been excessively hot and you've been sweating more than usual, or you've changed your laundry detergent or the type of deodorant you usually use.
Must be the heat cause haven't done anything else differant, thanks
Sweat can build up in your skin causing rashes.
new/expired deodorant, curtain clothing, heat