You know what it’s like to be sick. You feel fatigued, maybe a little depressed, less hungry than usual, more easily nauseated and perhaps more sensitive to pain and cold.
The fact that illness comes with a distinct set of psychological and behavioral features is not a new discovery. In medical terminology, the symptom of malaise encompasses some of the feelings that come with being ill. Animal behaviorists and neuroimmunologists use the term sickness behavior to describe the observable behavior changes that occur during illness.
Health care providers often treat these symptoms as little more than annoying side effects of having an infectious disease. But as it turns out, these changes may actually be part of how you fight off infection.
I’m an anthropologist interested in how illness and infection have shaped human evolution. My colleagues and I propose that all these aspects of being sick are features of an emotion that we call “lassitude.” And it’s an important part of how human beings work to recover from illness.
Your body sets priorities when fighting germs
The human immune system is a complex set of mechanisms that help you suppress and eliminate organisms – such as bacteria, viruses and parasitic worms – that cause infection.
Activating the immune system, however, costs your body a lot of energy. This presents a series of problems that your brain and body must solve to fight against infection most effectively. Where will this extra energy come from? What should you do to avoid additional infections or injuries that would increase the immune system’s energy requirements even more?
Fever is a critical part of the immune response to some infections, but the energy cost of raising your temperature is particularly high. Is there anything you can do to reduce this cost?