Your body sweats to regulate body temperature.
Underarm sweat is produced through two types of sweat glands located just below the surface of the skin. The eccrine glands secrete a clear, odorless fluid to help cool the body. The evaporation of sweat from the surface of the skin creates the cooling effect. The apocrine glands produce a thicker fluid that gives underarm sweat its distinctive odor.
For people who sweat excessively, the underarm sweat glands are overactive – frequently turning on when they should be at rest, and producing much more sweat than is needed to cool the body. In fact, some people’s sweat glands can produce four or five times more sweat than is normal.