This application provides a composition for preventing, alleviating and/or treating a heat illness, or cytotoxicity of cells such as vascular endothelial cells caused by load of heat stress and/or aberration associated with the production and release of a fever-inducing inflammatory cytokine(s) from blood cells caused by load of heat stress in a subject, comprising at least one substance selected from the group consisting of auraptene, tangeretin, and medium chain fatty acid as an active ingredient.