How chronic stress harms the body and when it becomes dangerous

Waking up late, checking a phone filled with distressing news, a child’s missing shoes, a bus lane fine — these everyday stressors trigger the same biological systems that evolved to handle physical threats like tribal conflicts or mammoth attacks. But when these systems remain activated continually, the consequences can be serious.

“The most immediate effect we see in a stressful situation is a surge of adrenaline causing an increase in heart rate, blood pressure and breathing,” said Prof Kavita Vedhara, a specialist in stress and behavioural medicine at Cardiff University. “This is your fight-or-flight response, and it’s designed to prepare you to address the challenge you are facing.”

Within about 30 minutes, cortisol — often reductively called the stress hormone — also rises. “Again, this is very useful in supporting the fight-flight response because it regulates blood pressure, suppresses inflammation and increases the availability of blood sugars to increase energy,” Vedhara said.

This system evolved for physical threats. Today, most stressors are psychological — online conflict, arguments — and the body diverts resources from digestion, repair and immunity (the rest-and-digest systems). Occasional activation is normal; chronic activation prevents recovery.

“Perhaps the most well-known issue associated with chronic stress is poorer immune function, which can increase risk of infections, make vaccines work less well, impair wound healing, and so on,” Vedhara said. “But chronic stress has also been shown to increase the risk of obesity, depressive illness and progression of neurodegenerative diseases such as Alzheimer’s.”

Chronic stress creates an unhealthy feedback loop. “Because of the complex physiological nature of the stress response, we often experience a range of changes in the body,” said Dr Jo Daniels, a senior lecturer in psychology at the University of Bath. “This in itself can become alarming for some people: why is my heart beating so fast? This can then trigger increased attention to what are essentially normal bodily variations, which effectively amplifies those physiological sensations, adding another layer of stress and anxiety.”

“When we’re in a stress response, we’re hypervigilant, so we’re more likely to consider normal variations in our bodily sensations to be threatening — and because we are flooded with stress hormones and we are using that ancient part of our brains that is programmed for survival, our decision-making is also likely to be impaired, so we might respond in ways that are unhelpful,” Daniels said.

“If you’re feeling a little on edge, for instance, perhaps you won’t go out, because it feels like your body is saying, ‘Something’s going on here that we need to protect ourselves against’,” Daniels added.

Scientists are still determining how much stress is too much. “It’s an elastic system — it’s designed to respond and recover,” Vedhara said. “How bad is it genuinely? It’s certainly true that the experience of stress has such wide-ranging effects on our physiology that there is potential for it to take a very real toll on our health and wellbeing — but that’s only true for long-term and enduring stressors.”

A landmark study in the 1990s found that among nearly 400 healthy volunteers exposed to the common cold, stress levels correlated strongly with illness. Older adults, with declining immune systems, may suffer worse effects from chronic stress than middle-aged people.

Individual tolerance varies significantly. “A lot depends on your life experiences,” Daniels said. “People who have been affected by trauma might have a lower threshold for stress response — while other people seem to seek out stressful careers and thrive in them. It is also influenced by learned resilience and ability to manage and respond to stress — though over the long term, as we saw during the Covid-19 pandemic, everyone has their limit.”

One evidence-backed strategy is learning to slow breathing. “When people are stressed or anxious, they tend to breathe in a more shallow and rapid way, which reinforces the threat response, keeping the physiological loop going,” Daniels said. “If you breathe slowly, you’re giving your brain the message that everything is OK, you are safe — essentially inducing the relaxation response. So something as simple as regulated breathing really can make a difference and head stress off at the pass.”

Exercise also helps reduce excess adrenaline buildup caused by high-stress responses, Daniels noted.

These techniques work best for acute (temporary) stress. For prolonged, disabling stress, evidence-based psychological therapies such as cognitive behavioural therapy (CBT) are recommended. “When stressed and overwhelmed, we often jump to thoughts like, ‘I can’t cope with this,'” Daniels said. “But is this true? Thoughts are not facts. A helpful strategy can be to sit down and assess the evidence — have you coped before? And with worse? Can you survive the worst-case scenario if you are late for school drop-off and forgot to feed the cat? It can also be useful to stop or phase out coping strategies that aren’t helpful and contribute to the problem — for example, some people tend to work longer or harder to try to solve a work-related problem, which is likely to contribute to increased stress over time.”

Mindfulness-based stress reduction takes a different approach: teaching skills to step back from unhelpful thoughts rather than challenge them.

Experts suggest experimenting with both approaches depending on the stressor. Negative thinking patterns and unhelpful coping strategies are often best tackled with CBT, while mindfulness-based stress reduction may be better for coping with unavoidable stressors.

Avoiding stress completely is unrealistic. Even the 6% of people in the UK who say they are never stressed likely manage challenging situations better than others. The best strategy for constant high stress is to identify and address its causes — from avoiding social media in the morning to changing jobs or difficult family conversations.

“Catch your stress response early, and you have a good chance of reversing it using simpler strategies — but for chronic stress, modifications to lifestyle, accessing social support and developing helpful coping skills are key,” Daniels said. “I would suggest people seek help when they are experiencing stress most or all of the time, or if they themselves are concerned about their stress levels.” And remember: while you cannot always control the mammoths charging at you, you can control how you respond to them.