Winter illnesses are all around us right now – from the common cold, COVID-19 and flu to strep throat and stomach bugs. They all have one thing in common: they can make you feel miserable. These diseases are often accompanied by fatigue, lack of appetite and difficulty concentrating. Sufferers often just want to be left alone, many people even experience sadness and anxiety.
Researchers have revealed why this happens. When your body is attacked by a pathogen, some of your immune cells recognize the pathogen and take action to eliminate the threat. To be successful, they must recruit other immune system cells as well as many organs in your body.
To do this, they secrete specific proteins, called cytokines. These are messengers, communicating the presence of a pathogen throughout your body, including him your mind.
Once the cytokine signal reaches your brain, it is activated changes in the activity of many brain structures. This leads to the development of fever, but not only.
These brain changes also lead you to they feel and act differently: you are much less motivated to do things you normally enjoy and prefer to be alone and in bed. Eventually, you feel tired and lack appetite. But you can also be more sensitive to negative stimuli, which can easily upset and upset you.
Credit: Julie Lasselin; ill: brgfx/Freepik, CC BY-SA
This means that the psychological experience of illness isn’t just triggered by your brain or the pathogen itself—it appears to be unleashed by your own immune system.
Make people sick for a day
How can we be sure that the feelings of illness are actually caused by our own immune system and not by the pathogen? Researchers have actually shown that such feelings can be caused without the presence of an actual pathogen.
My research group, and a few others around the world, deliberately activate the natural immune defenses of healthy young volunteers, without using a pathogen. In several of our experiments, we injected more than 100 study participants with a small dose of lipopolysaccharide, a component of the bacteria’s membrane Escherichia Coli. Because immune cells recognize this component as a pathogenic threat (even though there are no actual bacteria), they become activated and produce cytokines.
As during an actual infection, but without the presence of a pathogen, the cytokine signal reaches the brain and causes behavioral changes along with feelings of illness (collectively called “sickness behavior”).
Interestingly, our participants reported the same symptoms – malaise, fatigue and physical pain – no anti-infection. In the photos below, you can really see it they look less good after the injection.
Realization: Julie Lasselin
The participants said they would rather be at home than in our study room and were no longer interested in performing the various tasks we asked them to do. And although they weren’t particularly anxious or sad before the injection, several of the participants reported feeling anxious and sullen afterward.
Because there were no actual bacteria in the blood, and because the liver and immune cells quickly clear bacterial components from the blood, cytokine production lasted only a few hours, usually five to eight hours. And feelings of illness, including strong negative emotions that were triggered only a few hours earlier, also regressed within this time frame.
Why do we feel unhappiness during infections?
The question now is: should we feel sick during an infection? And if so, why? Well, even if you’re not fully aware of it, fighting a pathogen requires an incredible amount of energy. Both the activity of your immune cells and the increase in body temperature have a big impact. The only way your body can cope with these high energy demands is by greatly reducing the activity of organs that are not immediately needed.
Feelings of malaise ultimately drain your body’s energy it’s not being used for activities that are not necessary at the time of infection – you must be calm and stay at home. So they help you avoid using your muscles and even your brain – making you skip the gym or extended study. And feeling sad and anxious stops you from wanting to go out and party with your friends.
The feelings of illness are therefore is likely to be beneficial in combating the pathogen.
That’s probably the reason all vertebrateseven invertebrates such as bees and antswe behave as we do during infections.
So it can be difficult to just think of a way out of the frustration when you’re sick. But I hope this awareness will help you push away negative thoughts when faced with a winter illness. Don’t feel guilty or worried about feeling unhappy – it’s natural.
A healthy way of responding could actually be embracing these feelings as a normal response of your body when it needs to fight pathogens. If you don’t, chances are you’ll go down a spiral of guilt, fear, and negative emotions that keeps getting worse.
And by the way, if you feel miserable in the days after the vaccination… Don’t worry – it also means that your immune system is working.
