Тірі жануарлардың иісі және оның себептері

Odor produced by a living animal

Body odor or body odour (BO) is present in all animals and its intensity can be influenced by many factors (behavioral patterns, survival strategies). Body odor has a strong genetic basis, but can also be strongly influenced by various factors, such as sex, diet, health, and medication. The body odor of human males plays an important role in human sexual attraction, as a powerful indicator of MHC/HLA heterozygosity.

In humans, the formation of body odors is caused by factors such as diet, sex, health, and medication, but the major contribution comes from bacterial activity on skin gland secretions. In humans, the armpit regions seem more important than the genital region for body odor, which may be related to human bipedalism. The genital and armpit regions also contain springy hairs which help diffuse body odors. 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 pungent, cheesy and vinegar like smell although certain people might find it pleasant at lower concentrations. 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, gut microbiome, and genetics can affect body odor. For example, some animal species that 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. In most animals, body odor intensifies in moments of stress and danger.

In humans, body odor serves as a means of chemosensory signal communication between members of the species. These signals are called pheromones and they can be transmitted through a variety of mediums. The most common way that human pheromones are transmitted is through bodily fluids. Human pheromones are contained in sweat, semen, vaginal secretions, breast milk, and urine. Each person produces a unique spread of pheromones that can be identified by others. This differentiation allows the formation of sexual attraction and kinship ties to occur. Sebaceous and apocrine glands become active at puberty. This, as well as many apocrine glands being close to the sex organs, points to a role related to mating.

Pheromones are a factor seen in the mating selection and reproduction in humans. In women, the sense of olfaction is strongest around the time of ovulation, significantly stronger than during other phases of the menstrual cycle and also stronger than the sense in males. Pheromones can be used to deliver information about the major histocompatibility complex (MHC). Each type has a unique scent profile that can be utilized during the mating selection process. When selecting mates, women tend to be attracted to those that have different HLA types than their own. According to the researchers, this research suggests a possible role for human pheromones in the biological basis of sexual orientation.

Humans can olfactorily detect blood related kin. Babies can recognize their mothers by smell while mothers, fathers, and other relatives can identify a baby by smell. When compared to that of strangers, babies are observed to have stronger neural connections with their mothers. This strengthened neurological connection allows for the biological development and socialization of the infant by their mother. Using these connections, the mother transmits olfactory signals to the infant which are then perceived and integrated. While no specific human breast pheromones have been identified, studies compare the communication to that of the rabbit mammary pheromone 2MB2. The perception and integration of these signals is an evolutionary response that allows newborns to locate their source of nutrition. Signaling contains a level of precision that allows babies to differentiate their mother's breasts from that of other women.

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. Married couples are more different regarding MHC genes than would be expected by chance. This behavior pattern promotes variability of the immune system of individuals in the population, thus making the population more robust against new diseases. Another reason may be to prevent inbreeding.

Body odor may be reduced or prevented or even aggravated by using deodorants, antiperspirants, disinfectants, underarm liners, triclosan, special soaps or foams with antiseptic plant extracts such as ribwort and liquorice, chlorophyllin ointments and sprays topically, and chlorophyllin supplements internally. Although body odor is commonly associated with hygiene practices, its presentation can be affected by changes in diet as well as the other factors. Skin spectrophotometry analysis found that males who consumed more fruits and vegetables were significantly associated with more pleasant smelling sweat, which was described as "floral, fruity, sweet and medicinal qualities".

As many as 90% of Americans and 92% of teenagers use antiperspirants or deodorants. In 2014, the global market for deodorants was estimated at US$13.00 billion with a compound annual growth rate of 5.62% between 2015 and 2020.