The most common reason for excessive armpit sweating is due to hot and humid weather. However, there are some people who sweat excessively even in cold winter days. It may be caused by an illness like thyroid gland enlargement (hyperthyroidism) or a tumor that grows on the pituitary gland of the brain called prolactinoma which causes excess production of milk from your breasts (lactation). In such cases it is recommended to take extra medications like anticholinergic drugs commonly used as anti-spasmodics for temporary relief from itching and odor causing sweat glands. If you have any doubt about the cause of excessive underarm sweating look up symptoms on Google health app or ask your doctor first before taking any prescription medication especially if you suffer from other medical disorders including diabetes, high blood pressure, asthma etc..