The main cause is foot sweat. Sweat itself is odorless, but it creates a perfect environment for certain bacteria to grow and produce bad-smelling substances. Bacteria are naturally present on our skin. Foot odor is also the result of wearing shoes and/or socks with inadequate air ventilation for many hours. Because human feet are densely covered with sweat glands, perspiration of the feet can combine with surface bacteria to produce odor. Hair on the feet, especially on the toes, may contribute to the odor’s intensity by adding increased surface area in which the bacteria can thrive.
Body odor often abbreviated as B.O., or bromhidrosis (also called osmidrosis and ozochrotia and known alternatively as Apocrine bromhidrosis, Bromidrosis, Fetid sweat, Body smell, Malodorous sweating, and Osmidrosis) is the smell of bacteria growing on the body. These bacteria multiply rapidly in the presence of sweat, but sweat itself is almost completely odorless to humans. Body odor is associated with the hair, feet, hands, groin (upper medial thigh), anus, skin in general, armpits, genitals, pubic hair, belly button and ears (behind the ears).