If a rash only affects the right underarm, it may be an infection, as these more commonly affect one armpit rather than both. Shingles is a rash on one side of the body that feels painful and may ...

An armpit rash is often caused by irritation from sweat, friction, soap, or dryness. It could also be an allergic reaction to fragrances or propylene glycol (a deodorant ingredient). Other causes ...