Lassitude: The emotion of being sick

Joshua M. Schrock*, J. Josh Snodgrass, Lawrence S. Sugiyama

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

24 Scopus citations


Our long co-evolutionary history with infectious agents likely began soon after the rise of the first single-celled organisms. This ongoing evolutionary arms race has generated complex host adaptations, many highly conserved, for resisting infection (e.g., innate and acquired immune systems, infection-sensitive developmental programs, sexual reproduction). A large body of evidence suggests that, in humans, pathogen-avoidance disgust is an emotion that motivates avoidance of cues associated with pathogens, thereby reducing infection. However, the question of whether there is an emotion that coordinates resistance to active infection has received less attention. We propose that lassitude is such an emotion. It is triggered by cues of active infection and coordinates the fight against infection by: (a) reducing energetically expensive movement to make more energy available to the immune system, (b) reducing exposure to additional infections and injuries that would compound the immune system's workload, (c) promoting thermoregulatory behaviors that facilitate immunity, (d) regulating food consumption to be beneficial for the host but detrimental to pathogens, and (e) deploying strategies that elicit caregiving behavior from social allies. Lassitude exhibits the core features of an emotion – it is triggered by cues of an adaptive problem (i.e., infection), generates a characteristic facial expression (e.g., slack facial muscles, drooping eyelids, slightly parted lips), and has distinct qualia (e.g., profound tiredness, reduced appetite, feelings of vulnerability, altered temperature perception, increased pain sensitivity). We outline the information-processing structure of lassitude, review existing evidence, suggest directions for future research, and discuss implications of lassitude for models of human evolution.

Original languageEnglish (US)
Pages (from-to)44-57
Number of pages14
JournalEvolution and Human Behavior
Issue number1
StatePublished - Jan 2020


  • Consumption
  • Disease
  • Immunity
  • Motivation
  • Movement
  • Sociality

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Experimental and Cognitive Psychology
  • Arts and Humanities (miscellaneous)


Dive into the research topics of 'Lassitude: The emotion of being sick'. Together they form a unique fingerprint.

Cite this