Bromhidrosis is the medical term for an unpleasant body odour.
The body produces two very different types of sweat. About 2.5 million eccrine glands produce sweat all over the body in order to assist in regulating excessive body heat by evaporation, but apocrine glands produce a very different, oilier form of sweat in the armpits, groin, and around the nipples, that contains the sexually attractive pheromones.
Increased sweating obviously occurs with exercise and in hot weather, but it may also increase with stress. People who are suffering from long term or persistent stress may develop a noticeable body odour that disappears when the stress goes away. The hormonal changes associated with puberty, pregnancy and menopause may also cause a temporary increase in sweating.
Neither form of sweat has any significant smell but apocrine sweat is a good breeding ground for bacteria. It is the break-down of the oily apocrine sweat by bacteria that produces most body odour.