Does stress really lower your immune system?
Prolonged stress demonstrably lowers your immune system: fewer active immune cells, a weaker response to vaccines and a greater risk of infections. Short-term stress has precisely the opposite effect and makes your immune system briefly more alert.
Short-term stress does not lower your immune system -- it actually gives it a temporary boost. Immune cells such as natural killer cells (NK cells) and T cells are mobilised and sent to sites of infection or inflammation. From an evolutionary standpoint that makes sense: your body is preparing itself for a threat.
With prolonged, chronic stress, the picture reverses completely. The activity of those killer cells demonstrably declines, you produce fewer antibodies, and the protection you receive from vaccinations becomes weaker. This effect has been found consistently across multiple independent studies, including in people who provide long-term informal care or are exposed to occupational stress.
The main culprit behind prolonged stress is largely the stress hormone cortisol. Persistently high cortisol levels slow wound healing, weaken the response to vaccines and suppress the protective cells of the immune system. In addition, dormant viral infections, such as herpesviruses, can resurface under stress because immune control over them diminishes.
There is a further, less intuitive effect: chronic stress causes a smouldering, low-grade inflammatory state in the body. That may sound like 'more immune activity', but it works against you. The immune system is constantly ticking over at a low level without responding effectively at the right moment. This state is associated with a greater risk of infections, but also with broader health problems such as cardiovascular disease and metabolic disorders.
In short: the distinction between short and long is crucial. A nerve-wracking presentation makes your immune system briefly more alert. Months of sustained pressure do the opposite, and that damage is measurable -- including in your blood values and your response to a flu vaccine.
This answer is based on several large review studies and one analysis that pools data from multiple studies. The evidence for chronic stress as an immune suppressant is broadly supported and consistent across different study populations. The evidence for acute stress as a temporary immune booster is somewhat less in-depth but has been described consistently. The association between stress and herpesvirus reactivation is convincing but rests on an association, not a demonstrated cause-and-effect chain in humans. The link with cancer is preliminary and speculative.
What does sleep deprivation do to your immune system?
Sleep deprivation demonstrably weakens your immune system: sleeping fewer than six hours significantly increases your infection risk and impairs your immune cells. Make sure to structurally get seven hours or more, because a single recovery night is not enough to repair the damage.
Can air pollution weaken your immune system?
Air pollution disrupts your immune system in several ways at once: a greater chance of allergic reactions, less resistance to viruses. Limit your exposure as much as possible, especially during pregnancy.
Does your immune system really weaken as you get older?
Your immune system does indeed weaken as you get older, but how quickly that happens varies considerably from person to person. Lifestyle factors play a role in this, although little has yet been proven specifically for humans.
Does cold showering boost your immune system?
Cold showering produces measurable stimulation of the immune system, but whether it actually makes you less likely to fall ill has not been proven. Until better research is available, there is no harm in doing it if you enjoy it, but do not count on it as protection against infections.
Does your immune system really weaken as you get older, and can you do anything about it?
Your immune system demonstrably weakens with age, but eating healthily and exercising can reduce the smouldering inflammation that accompanies it. It is still too early to rely on drugs targeting senescent cells.
How do I strengthen my weakening immune system?
You can partly support your immune system by correcting measured deficiencies in vitamins and minerals and by making use of vaccines specifically tailored for older adults. More far-reaching options such as experimental inhibitors are not yet safe enough for daily use outside of studies.