Sweat smells like vinegar because of propionic acid produced in the ducts of sebacious glands. This acid is a byproduct of amino acids that are broken down by a bacterium that lives in these ducts, according to Medical News Today.
The human skin provides a favorable environment for the growth of a variety of microorganisms. Its grooves, folds, moisture and dark areas, allow certain bacterium, fungi and even mites to live on the surface of human bodies, according to the National Center for Biotechnology Information. Propionibacterium acnes is one these commensal organisms, and it's responsible for the production of ingredients that make sweat smell like vinegar. In certain conditions, this bacterium becomes pathogenic and plays an important role in the development of acne. Another bacterium that lives on the skin is Staphylococcus epidermidis, which gives sweat a strong cheesy smell because of its production of isovaleric acid.
Many people use deodorants or antiperspirants to eliminate the strong smell of sweat, according to Medical News Today. Deodorants help eliminate smells by making the environment too acidic for the bacteria as well as by masking already existing smells with fragrance. Antiperspirants reduce smells by preventing the action of sweating. More invasive therapies involve injections of Botulinum toxin into sweat glands, paralyzing the muscles responsible for the excretion of sweat.