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 types of strong cheese. Factors such as food, drink, and diseases can affect body odor, as can lifestyle and genetics. Function
Animals
In many animals, body odor plays an important survival function. Strong body odor can be a warning signal for predators to stay away (such as porcupine stink), or it can also be a signal that the prey animal is unpalatable. For example, some animals species, who feign death to survive (like opossums), in this state produce a strong body odor to deceive a predator that the prey animal has been dead for a long time and is already in the advanced stage of decomposing. Some animals with strong body odor are rarely attacked by most predators, although they can still be killed and eaten by birds of prey, which are tolerant of carrion odors.Body odor is an important feature of animal physiology. It plays a different role in different animal species. For example, in some predator species that hunt by stalking (such as big and small cats), the absence of body odor is important, and they spend plenty of time and energy to keep their body free of odor. For other predators, such as those that hunt by visually locating prey and running for long distances after it (such as dogs and wolves), the absence of body odor is not critical.
The genital and armpit regions also contain springy hairs which help diffuse body odors.The main components of human axillary odor are unsaturated or hydroxylated branched fatty acids with E-3M2H (E-3-methylhex-2-enoic acid) and HMHA (3-hydroxy-3-methylhexanoic acid), sulfanylalkanols and particularly 3M3SH (3-methyl-3-sulfanylhexan-1-ol), and the odoriferous steroids androstenone (5α-androst-16-en-3-one) and androstenol (5α-androst-16-en-3α-ol). E-3M2H is bound and carried by two apocrine secretion odor-binding proteins, ASOB1 and ASOB2, to the skin surface.Body odor is influenced by the actions of the skin flora, including members of Corynebacterium, which manufacture enzymes called lipases that break down the lipids in sweat to create smaller molecules like butyric acid. Greater bacteria populations of Corynebacterium jeikeium are found more in the armpits of men, whereas greater population numbers of Staphylococcus haemolyticus are found in the armpits of women. This causes male armpits to give off a rancid/cheese-like smell, whereas female armpits give off a more fruity/onion-like smell. Staphylococcus hominis is also known for producing thioalcohol compounds that contribute to odors. These smaller molecules smell, and give body odor its characteristic aroma. Propionic acid (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 characteristics including odor, body odors may be identified as having a vinegar-like smell by certain people.