How stress can affect your health

Posted on 24/9/2021

By Professor Kavita Vedhara, Professor of Health Psychology, University of Nottingham.

Stress is a term that we all use in our everyday lives.

In recent years, general awareness of how stress can impact our health has increased hugely.

Stress is now the focus of bestselling books, front covers of magazines, mainstream chat shows and television programs. And now, perhaps more than ever, stress is now recognized as being a major factor that can affect every aspect of our health and well-being.

Stress is, to put it mildly, everywhere!

But, what actually is stress? How can it affect your health? And, what does cortisol have to do with it?

What is stress?

There are many definitions of what stress is and what one person finds stressful another may not. However, in general terms, ‘stress’ can best be thought of as an ‘experience’ which is triggered by an event (in the past, present or future) which an individual perceives as potentially being threatening. In this way, the experience of stress is part emotional (impacts on how you feel), part cognitive (impacts on what you think), part behavioural (impacts on how you behave) and part physiological (impacts on core biological functions such as your heart rate, blood pressure and the release and regulation of hormones).

Stress can be short-lived (‘acute’) or long lasting (‘chronic’.). Acute stressis, by definition, transient (eg having a driving test, going for an interview) and so is not usually associated with negative effects on health. Infact some research shows that acute stress can have beneficial effects. Chronic stress is more long-term (e.g., unemployment, bereavement, caring for others) and can result in physiological wear and tear referred to as ‘allostatic load’ and may have a range of serious consequences for our health.

What happens when we feel stressed?

When we encounter a stressful situation our body produces a cascade of physiological responses that serve together to give you the energy you need to ‘fight or flight.

There are two main systems that are activated when we experience stress. The first is the sympathetic–adrenal–medullary (SAM) system. The second is the hypothalamic–pituitary–adrenal (HPA) axis.

Key changes you may observe when the SAM system is activated include your breathing quickening, increases in heart rate,eyes dilating to aid vision and ‘non essential’ processes such as activity of the digestive system turn off to permit more blood to go to the muscles and energy to be spent dealing with the stressful situation.

The HPA axis serves to provide further energy resources to help deal with the stressful experience.

It starts with your hypothalamus releasing corticotrophin releasing factor (CRF) which is transported in the blood supply to the pituitary gland, where it stimulates the release of adrenocorticotrophic hormone (ACTH). ACTH stimulates production of the glucocorticoid cortisol, the so-called ‘stress hormone’.

How can stress affect your health?

Decades of high quality research has shown, time and again - that chronic stress can have serious consequences for your health now, and in the future.

Stress can affect your health directly through a range of processes inside your body, but also indirectly through changing your health behaviors such as your diet, lifestyle habits, exercise and sleep.

Stress has been shown to affect everything from how well vaccinations work to your longevity.

Some ways chronic stress can impact your health...

  • Affect how well your body responds to vaccines
  • How well you recovery from surgery
  • Change your risk of heart disease
  • Affect Fertility
  • Impact on brain health and cognitive function

How can measuring cortisol help?

One of the pernicious features of stress, particularly when it is chronic stress, is that we often don’t recognize when we are experiencing it. The changes in how we feel, think and behave happen slowly over time and so often we don’t realise we are stressed until the feelings become overwhelming. We may not realise the effects on our health until some damage is done.

Measuring cortisol is one way to get some early insight into how much stress you are experiencing

There are several ways to measure cortisol,such as through samples of blood, saliva and urine. But all of these have in common that they only capture your short-term cortisol levels over durations from minutes to hours.

But these ‘snap shots’ of cortisol can be misleading because cortisol levels go up and down in response to lots of factors. It is only when cortisol levels are raised for long periods of time, as we see during chronic stress, that the effects may be harmful for health. So in an ideal world, a measure of cortisol wouldn’t just tell you about the last few minutes or previous day, but over much longer periods of time. This is possible when you measure cortisol in hair.

Assessing cortisol in hair provides a cumulative ‘timeline’ of your cortisol levels over several months, providing an extremely accurate, reliable and more practical way of assessing long term levels of the hormone.

Empowering you to take control of your stress

The benefit of assessing your cortisol levels is that by knowing how your body may be responding to stress on the inside, you can take a number of actions to help improve your health and well-being.

It is important to bear in mind that cortisol is a complex hormone and beyond it’s role in the stress response it is also affected by your overall lifestyle.

This is good news because it means that in addition to taking action to reduce your stress, you may also improve your cortisol levels through a combination of lifestyle changes such as your diet, sleep, and getting the right amount of exercise.

Remember, what works for you will be unique and you don't have to try and make changes to your lifestyle all at once. Small changes to your lifestyle can help you manage stress, improve your lifestyle, your health and your overall well being.

To ask a question about stress then you can get in touch at

For those wanting a comprehensive recent overview of stress and health please see

O’Connor,D., Thayer, J., and Vedhara,K. (2020). Stress and Health: A review of psychobiological processes. Annual Review of Psychobiological Processes. Annual review of Psychology, 72, 4.1-4.26.


Greff, M et al. 2019. Hair cortisol analysis: An update on methodological considerations and clinical applications. Clinical Biochemistry, 63, 1-9.

Lovallo WR. 2016. Stress and Health: Biological and Psychological Interactions. Thousand Oaks, CA: SAGE. 3rd ed.

O’Connor,D., Thayer, J., and Vedhara,K. (2020). Stress and Health: A review of psychobiological processes. Annual Review of Psychobiological Processes. Annual review of Psychology, 72, 4.1-4.26.

Raul J-S, Cirimele V, Ludes B, Kintz P. 2004. Detection of physiological concentrations of cortisol and cortisone in human hair. Clin. Biochem. 37:1105–11

Segerstrom SC,Miller G. 2004. Psychological stress and the human immune system: a meta-analytic study of 30 years of inquiry. Psychol. Bull. 130:601–30

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