Allogrooming

Allogrooming is a social grooming behavior in which one individual cleans, inspects, or preens the body of another. It is distinguished from autogrooming, which is grooming performed on oneself. Allogrooming is observed in many group-living animals, especially primates, and serves a combination of hygienic and social functions.

The primary hygienic function is parasite removal and skin maintenance, which can reduce irritation and ectoparasite load. Beyond cleanliness, allogrooming plays a crucial role in social bonding, tension reduction, and the formation and maintenance of alliances. It can function as reconciliation after conflict and as a mechanism for soliciting cooperation or support within a social network. In some species, grooming also signals affiliation and can influence access to resources or mating opportunities through its role in status and bond-building.

Direction and frequency of allogrooming are influenced by social structure. Grooming tends to be more frequent among kin or close associates, and reciprocal grooming is common: individuals who groom others often receive grooming in return. Grooming networks can reflect and reinforce dominance hierarchies and social ties, shaping group cohesion and stability.

Physiological and fitness implications include associations with hormonal changes that promote bonding and stress reduction, such as lowered cortisol and elevated oxytocin or endorphins in some species. However, allogrooming entails costs, including time and energy expenditure and potential disease transmission, and may be used opportunistically by individuals to gain favor or soften social tensions.

Empirical work on allogrooming is extensive in primates such as chimpanzees, baboons, macaques, and capuchins, and observations extend to other social mammals. It remains a key indicator of social structure, cooperation, and welfare in both wild and captive populations.