A combination of sweat produced by the apocrine glands and bacteria breaking down keratin protein on the surface of the skin cause underarm odor. Eccrine sweat softening keratin protein on the skin's surface is another potential cause of underarm odor.
Underarm odor can also be caused by consuming certain foods, such as garlic, onions, hot chili peppers, fish and curry. Consuming other types of spicy foods, alcohol and red meat can also make underarm odor worse. Underarm odor, also known as bromhidrosis, can also be caused by certain health issues, such as obesity and diabetes. These conditions cause underarm odor because they are associated with other conditions that encourage the growth of bacteria.
The apocrine glands open into the hair follicles, where they secrete a thicker type of sweat typically connected to underarm odor. Apocrine glands are generally located in areas of the body that are warm and confined. The moisture generated in these confined areas becomes the breeding ground for bacteria that causes body odor. Sweat itself is basically odorless; the odor that is created comes from the products that are created as bacteria breaks down keratin proteins. Odor can occur in other areas of the body as well, such as the groin, anal area, upper thighs, feet and any other area of the body that is prone to sweating.