Boob sweat can occur for several reasons. Your body temperature may be high, your hormones are changing or your skin could be irritated. Sweating is a way for our bodies to naturally control it's body temperature. Under-boob sweat is a common problem for women, when the area under the breasts is warm and moist, it can be the perfect breeding ground for bacteria and fungus, which can lead which can lead to skin irritations, body odour and rashes. It can be more common for women with larger breasts due to extra skin which can hand loosely over the chest; but it can affect anyone.