Sickness behavior

Sickness behavior, sometimes called sickness response, are nonspecific behavioral changes humans and many animals adopt in response to an infection. Responses include lethargy, lack of appetite, low grade fever, sleepiness and lack of motivation. It is thought to have evolved to encourage behaviors that conserve energy and allow the host to better mount an immune response against invading pathogens.

Immune response
In response to the presence of a pathogen, proinflammatory cytokines IL-1, IL-6 and tumor necrosis factor (TNF) are released peripherally. These may then be sensed by the vagus nerve initiating a set of behavioral responses in the brain.

Learn more

 * "Vertebrate sickness behaviors: Adaptive and integrated neuroendocrine immune responses", Integrative and Comparative Biology, Volume 49, Issue 3, September 2009
 * "When is it socially acceptable to feel sick?" (review article), Proceedings of the Royal Society B, August 7, 2014
 * "Sickness behavior : immune system influences on brain and behavior" (series of three papers), Karolinska Institutet, Sweden, May 29, 2015
 * "It's Not Just A Cold, It's 'Sickness Behavior'", NPR, January 6, 2018