Body odor a.k.a bromhidrosis (also called bromidrosis, osmidrosis and ozochrotia) is the smell of bacteria growing on the body. Those bacteria multiply rapidly in the presence of perspiration. However, sweat itself is almost completely odorless. Body odor is associated with armpits, the hair, feet, groin (upper medial thigh), anus, skin in general, genitals, and mouth.
Body odor can smell lovely and specific to the individual, and can be used to identify people, though this is more often done by animals, than by humans. An individual’s body odor is also influenced by diet, gender, genetics, health, medication, and mood.
Propionic acid or propanoic acid is present in many sweat samples. This acid is a breakdown product of some amino acids by propionibacteria, which thrive in the ducts of adolescent and adult sebaceous glands. Because propionic acid is chemically similar to acetic acid with similar physical characteristics including odor, body odors may be identified as having a vinegar-like smell by certain persons.
Isovaleric acid (3-methyl butanoic acid) is the other source of body odor as a result of actions of the bacteria Staphylococcus epidermidis, which is also present in several sharp cheese types.
Mainly, the body odor is influenced by major histocompatibility complex (MHC) molecules. These are genetically determined and play an important role in immunity of the organism. The vomeronasal organ contains cells sensitive to MHC molecules in a genotype-specific way.
Experiments on animals and volunteers have shown that potential sexual partners tend to be perceived more attractive if their MHC composition is substantially different. This behavior pattern promotes variability of the immune system of individuals in the population, thus making the population more robust against new diseases.
A recent study suggests that body odor is genetically determined by a gene that also codes the type of earwax one has. East Asians evidently have a greater chance of having the ‘dry’ earwax type and reduced axial sweating and odor. This may be due to adaptation to colder climates.