In social animals, including humans, social grooming or allogrooming is an activity in which individuals in a group clean or maintain one another's body or appearance. It is a major social activity, and a means by which animals who live in proximity can bond and reinforce social structures, family links, and build relationships. Social grooming is also used as a form of reconciliation and a means of conflict resolution in some species.
It is a reuse of ordinary grooming behavior, a means of achieving hygiene and good health, in that an animal that helps another animal to clean itself, is also helping to form a social bond and trust between them.
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Animals regularly clean themselves to keep their fur, feathers, scales, or other skin coverings in good condition. This activity - known as personal grooming, preening, or auto-grooming - promotes hygiene. Dead skin and foreign objects such as insects, ectoparasites, and leaves, dirt and twigs, are some of the items typically removed.
Many social animals groom each other, an activity known as social grooming, mutual grooming, or allo-grooming. Items removed during social grooming are identical to those removed by personal grooming. Social grooming also takes the form of stroking, scratching, and massaging.
Primates provide perhaps the best example of this activity. Primatologists have called grooming the social cement of the primate world. The trust and bonding it builds is critical to group cooperation. Among primates, social grooming plays an important role in establishing and maintaining alliances and dominance hierarchies, for building coalitions, for reconciliation after conflicts, and is a resource that is exchanged for other resources, like food and sex.[1][2][3][4] Primates groom socially in moments of boredom as well, and the act has been shown to reduce tension and stress.[5] It is often associated with observed periods of relaxed behaviour, and primates have been known to fall asleep while receiving grooming.[6]
Results of a research shows that male Crab-eating Macaques will groom females in order to get sex. The study found that a female has a greater likelihood to engage in sexual activity with a male if he had recently groomed her, compared to males who had not groomed her.[7]
Other animals groom socially as well. These include insects,[8] fish,[9] birds,[10] ungulates,[11] and bats.[12] Whereas social grooming among primates has been very well-studied, less is known about social grooming in these other animals.
Mammals often perform social grooming. Domesticated animals, especially cats and dogs, will groom trusted humans as a sign of affection.
A few empirical studies of human social grooming exist.[13][14] They rely on self-report survey and experimental methodology of adults living primarily in the U.S. and other Western cultures. People report grooming romantic partners more than grooming people they have other types of relationships with like family members, friends, and strangers. Grooming is associated with increased relationship satisfaction, trust, and experience of family affection while growing up. People who groom, as opposed to touch each other without grooming, are perceived to be better potential parents, more in love with the person they have groomed and more caring and committed to them. Women, but not men, tend to think people who have groomed one another are romantically involved. People also think that if people who have groomed one other are romantically involved, they are in a long-term relationship rather than one that has just begun. Human mutual grooming plays a role in pair-bonding.
Grooming stimulates the release of beta-endorphin, which is one physiological reason for why grooming appears to be relaxing.[15]
Additionally, an article published in 1997 concluded that an increase in maternal grooming resulted in a proportionate increase in Glucocorticoid receptors on target tissue in the neonatal rat. Additionally, it was found that the receptor number was altered because of a change in both serotonin and thyroid-stimulating hormone concentrations. An increase in the number of receptors might influence the amount of negative feedback on corticosteroid secretion and prevent the undesirable side effects of an abnormal physiologic stress response.[16]