We all sweat. It's our body's way of cooling us down. Sweat doesn't stink, yet we do. Why is that? The zinc oxide Mum used suggests that the 19th-century inventor knew that bacteria, not perspiration itself, made underarms reek. Zinc oxide is an antibacterial. Bacteria were relatively new concepts at the time, which makes Mum's reasoning (if he so reasoned) more than amazing. Since then, scientists have figured out that bacteria feeds on some of the substances in sweat, thereby causing our bodies to smell. Your underarms are ground zero.
Underarms brim with apocrine glands, one of two main types of sweat glands that cover your body. Usually found in areas laden with hair follicles, apocrine glands produce a milky perspiration comprising water, proteins, lipids, fatty acids, cholesterols and iron-containing salts. When you perspire, the walls of the apocrine glands shrink, allowing the fluid to glom onto your hair follicles. The perspiration, which at this point is odorless, eventually pushes its way to the surface of the skin, escaping through the tiny openings of the hair follicles. Bacteria take notice and begin devouring the protein and fatty acids in the sweat. The stench is the result of bacterial breakdown [source: Mayo Clinic].
Deodorants and antiperspirants are the first line of defense against body odor (as is taking a shower and bath), yet don't get the two confused. Although we use the names interchangeably, each has its own method of dealing with body odor. The chemicals in antiperspirants, such as aluminum chloride or aluminum hydroxybromide, keep you from sweating. They permeate the cells that line the ducts of the sweat glands near the epidermis, the top layer of the skin. The chemicals and water are then drawn down into the cells, causing the sweat ducts to swell and become obstructed. That prevents some perspiration from migrating to the surface of the skin. The less you sweat, the less food there is for bacteria to devour. Hence, the less you smell [source: Poucher].