It's a common belief that high stress levels can make you more susceptible to catching a cold or flu. But what does the science actually say about the link between your mental state and your physical defences?
The Critical Difference: Short-Term Panic vs. Long-Term Strain
According to Professor Daniel M Davis, head of life sciences at Imperial College London, stress undeniably influences immune health, but the type of stress matters greatly. "Stress is a very broad phenomenon," Davis explains. "You can feel stressed watching a horror movie, or you can experience long-term stress, like going through a divorce."
Short-term, acute stress causes a temporary shift. The number of immune cells in your bloodstream can change during a stressful event. However, this is typically a fleeting reaction. "It returns to normal within about an hour," says Davis, "so it's unlikely to have any major impact on your likelihood of getting sick."
How Chronic Stress Actively Suppresses Immunity
The real danger to your health comes from prolonged, chronic stress. When your body is under sustained pressure, it perceives a continuous threat. This triggers the adrenal glands to release hormones, including adrenaline and the steroid hormone cortisol, as part of the ancient 'fight or flight' response.
While this reaction increases heart rate and blood pressure to deal with immediate danger, it also has a significant downside: it suppresses the immune system. Davis, author of 'The Secret Body: How the New Science of the Human Body Is Changing the Way We Live', notes this effect is visible at a cellular level. "If we take immune cells and expose them to diseased cells, like cancer, the immune cells will usually destroy them. But if we add cortisol, they become much less effective."
When exposure to elevated cortisol continues for weeks or months, this dampening effect persists, leaving the body's defences diminished and more vulnerable to infection and illness.
Managing Stress for Better Immune Health
Research indicates that stress-reduction practices such as mindfulness meditation and tai chi can help lower cortisol levels, which in theory should support a stronger immune response. However, Davis points out that definitively proving this link in real-world settings is complex. You cannot ethically expose large groups of people to pathogens to test their resilience, and measuring overall "immune health" outside a lab is challenging.
"It's also hard because you can't avoid stress," he adds. "Every change in our life will have some stress associated with it, and a lot of changes are positive." The goal, therefore, is not to eliminate stress entirely but to manage chronic, unhelpful stress.
For individuals concerned about the impact of long-term stress on their health, Professor Davis recommends speaking to a GP as a first step. Medical professionals can provide guidance on managing persistent stress and its physical manifestations, ensuring that both mind and body receive the support they need.
