Armpit Odor is caused by bacteria (which lives normally on skin) feeding on the secretions from your sweat glands. There are actually two different types of sweat. The watery cooling type produced by the ecrine glands and a milky thicker type from the apocrine glands. There are two to three million eccrine glands covering our body, and eccrine sweating starts from birth. Babies skins are covered with apocrine glands – this is why they have such a distinctive smell. Most of these glands stop working several months after birth, however, and until the start of puberty, at around eight years old for girls and nine years old for boys. In adults, apocrine sweat glands number a mere 2000 or so and are concentrated in the groin and armpits, although there are also some on the scalp and elsewhere. Apocrine secretion is stimulated by hormones and is triggered by fear and stress. Stress sweating occurs mainly in the underarm areas, feet and palms (this phenomenon is exploited by lie detector machines). It’s the apocrine secretion that causes the armpit odor problem. Certain anaerobic bacteria (corynebacteria and micrococci) consume this stuff and produce the pungent armpit odor we have been taught to be embarressed about in ourselves and detest in others for its social stigma.