What happens inside you

There is a prevailing notion that what doesn't kill you, makes you stronger. It suggests that surviving a disease can leave you in a better state. This idea seems logical because many of us have experienced increased resilience and preparedness after going through hardships. However, it turns out that sometimes surviving an illness can actually weaken you. So, what exactly happens when you fall sick?

Let's think of your body as a large country with a substantial army defending it. Imagine being surrounded by enemies who are after your land, energy, and resources. Given the life-and-death nature of the situation, your body has evolved to be highly sensitive to damage and the presence of adversaries. It needs to act swiftly because an invasion could occur at any moment.

Now, let's initiate an invasion and observe the consequences. As soon as your cells detect that something is amiss, they release a barrage of signal proteins called cytokines. These cytokines act like air raid sirens, activating various immune cells that, in turn, release more cytokines, intensifying the alarm. Soon, your system is flooded with signals triggering precautions and countermeasures. Mobilization is underway.

In response, your brain initiates sickness behavior and reorganizes your body's priorities to prioritize defense. The first noticeable change is a drop in energy levels and increased drowsiness. You may feel apathetic, anxious, or down, and your appetite may decrease. Your sensitivity to pain heightens, and you seek rest. All these changes serve to conserve energy and redirect it towards your immune response.

Essentially, you become a country under attack, transitioning into a war economy. Activating your immune system fully is disruptive and draining, much like the costs of war for a nation when industries shift their focus to building tanks. Your immune system demands significant amounts of energy, amino acids, and microelements to construct its weapons. For instance, fever speeds up your metabolism, making cells work harder and faster while generating heat that stresses many invaders. However, maintaining this state requires a substantial number of calories.

Simultaneously, your immune system begins cloning millions of specialized immune cells to specifically combat the invading pathogen. B cells generate millions of antibodies every second, each requiring hundreds of amino acids to assemble. Billions or even trillions of proteins need to be synthesized to refresh the complement system, a crucial defense mechanism within your blood. Cytokines, the mobilization and information signals, also need constant renewal.

Typically, you acquire these resources through eating. However, when you're sick, your body slows down digestion because it requires a significant amount of energy that you cannot spare. Consequently, it taps into the easiest source of amino acids, breaking down your muscles. All the hard-earned muscle you've developed is sacrificed to sustain your life.

If you're young, healthy, and fit, you'll quickly recover and replenish the lost muscle once you're better. However, if you're old, very young, weak, or have a chronic illness, this energy drain can be overwhelming. Your body literally consumes itself to sustain the defense. When your system is already strained, falling sick can push your capacities to the limit. Unfortunately, your immune system can be as harmful to your body as it is to the invaders. Achieving a delicate balance between infection damage and collateral damage caused by immune cells is a challenge.

Neutrophils, your first responders, can be likened to highly aggressive chimps armed with machine guns. When encountering enemies, they release chemicals that not only attack the invaders but also harm healthy cells, especially when the patient is already compromised, such as from smoking. Additionally, the microorganisms invading your body often release chemicals and toxins that can cause significant damage and cell death. As a result, a serious infection can leave tiny