Sweat itself is virtually odorless to humans. It is the rapid multiplication of bacteria in the presence of sweat and their breaking down of sweat into acids that eventually causes the unpleasant smell.
When a body gives off a scent other may find unpleasant, it is known as body odor.
Body odor usually becomes evident if measures are not taken when a human reaches puberty. People who are obese, those who regularly eat spicy foods, as well as individuals with certain medical conditions, such as diabetes, are more susceptible to having body odor.