Stress is a normal part of life. When we face a challenge, threat or period of uncertainty, our bodies respond automatically to help us cope.
In the short term, this stress response can be useful. It can make us more alert, focused and ready to act. But when stress continues for weeks or months without enough opportunity to recover, it can begin to affect both our physical and mental health.
One of the systems involved in this process is the hypothalamic-pituitary-adrenal axis, more commonly known as the HPA axis.
What is the HPA axis?
The HPA axis is one of the body’s main stress-response systems. It involves three parts of the body working together:
- The hypothalamus, in the brain
- The pituitary gland, also in the brain
- The adrenal glands, which sit on top of the kidneys
When your brain detects a perceived threat or challenge, several stress-response systems are activated.
The sympathetic nervous system produces the rapid “fight or flight” response associated with increased heart rate, faster breathing and the release of adrenaline.
At the same time, the HPA axis triggers a hormonal chain reaction. The hypothalamus signals the pituitary gland, which in turn signals the adrenal glands to release cortisol.
Cortisol helps the body mobilise the energy and resources it needs to respond.
What does cortisol do?
Cortisol is sometimes described as the “stress hormone”, but that can make it sound as though cortisol itself is harmful.
In fact, it’s essential, giving you the energy to get up in the morning, focus during the day, and respond to challenges.
Cortisol plays a role in many normal bodily functions, including:
- Regulating energy and metabolism
- Helping control blood sugar
- Supporting the body’s response to stress
- Regulating inflammation and immune activity
- Helping maintain our natural sleep-wake cycle
Under healthy conditions, cortisol levels follow a natural curve.
They rise sharply in the morning, giving your body energy and alertness, then gradually taper down during the day, preparing you for rest at night.
What happens when stress becomes chronic?
When we live under chronic stress- emotional, physical, or even hidden physiological stress like inflammation- that rhythm flips or flattens.
Long-term stress can affect the activity of the HPA axis and other biological systems involved in mood, sleep, immunity and metabolism.
The effects are not the same for everyone. There isn’t one particular cortisol pattern or set of symptoms that shows that someone’s HPA axis is “out of balance”.
However, chronic stress can contribute to a wide range of physical and emotional difficulties.
How chronic stress can affect the body and mind
Stress does not only affect how we feel emotionally. It can affect sleep, concentration, appetite, energy levels and physical health.
Some people experiencing prolonged stress may notice:
Sleep and energy
- Difficulty falling or staying asleep
- Waking feeling unrefreshed
- Feeling tired during the day
- Finding it difficult to switch off at night
- Relying increasingly on caffeine to stay alert
Mental and emotional wellbeing
- Feeling anxious or on edge
- Becoming overwhelmed more easily
- Irritability
- Low mood
- Difficulty concentrating
- Forgetfulness or “brain fog”
- Finding it harder to recover after stressful events
Physical symptoms
- Headaches
- Muscle tension
- Digestive problems
- Changes in appetite
- Changes in energy levels
- Increased awareness of aches and pains
- Feeling generally run down
Behavioural changes
You may also notice changes in how you respond to everyday life, such as:
- Withdrawing from other people
- Exercising less
- Eating more or less than usual
- Increased use of caffeine, alcohol or other substances
- Finding it harder to maintain normal routines
- Avoiding tasks that would usually feel manageable
These symptoms can have many different causes and do not necessarily mean there is a problem with cortisol or the HPA axis.
If symptoms are persistent, worsening or affecting your everyday life, it is important to speak to your GP or another healthcare professional.
The HPA axis and mental health
Researchers have studied the HPA axis extensively in relation to mental health.
Changes in HPA-axis activity have been identified in groups of people experiencing conditions including depression, anxiety and post-traumatic stress disorder (PTSD).
However, the relationship is complex.
Mental health difficulties are not caused by a single hormone or biological system, and cortisol levels cannot be used on their own to diagnose anxiety, depression, or PTSD.
The HPA axis is better understood as one part of a much larger picture involving the brain, nervous system, hormones, environment, relationships, experiences and genetics.
Depression
Research suggests that some people experiencing depression have changes in the way the HPA axis responds to stress.
This may help explain why depression can affect much more than mood. People may also experience fatigue, sleep disturbance, difficulty concentrating and changes in appetite.
Anxiety
Anxiety can activate the body’s threat-detection systems even when there is no immediate physical danger.
This is why anxiety may produce very real physical symptoms such as a racing heart, sweating, muscle tension, stomach problems or difficulty sleeping.
PTSD
Trauma can affect the body’s response to future threats.
People with PTSD may remain highly alert to danger, experience powerful physical reactions to reminders of trauma or find it difficult for their nervous system to settle after becoming activated.
Research continues into how the HPA axis and other stress-response systems contribute to these experiences.
How can I support a healthy stress response?
There is no single technique for “resetting” the HPA axis.
Instead, the most useful approach is to reduce prolonged stress where possible and give the body regular opportunities to recover.
Helpful strategies can include:
- Maintaining a regular sleep routine
- Getting regular physical activity
- Eating regularly and maintaining a balanced diet
- Practising breathing exercises, mindfulness or relaxation techniques
- Spending time outdoors
- Staying connected with supportive people
- Taking regular breaks during demanding periods
- Setting boundaries around work and other responsibilities
- Reducing reliance on alcohol or other substances as a way of coping
- Making time for activities that help you feel calm or engaged
Stress management does not mean removing every source of stress from your life.
Instead, it means recognising when pressure has become prolonged or overwhelming and finding ways to help your body and mind recover.
When stress is more than “just being busy”
It can be easy to dismiss persistent exhaustion, anxiety, poor sleep or difficulty concentrating as simply being busy.
But if stress is beginning to affect your work, relationships, physical health or ability to enjoy everyday life, it may be worth seeking support.
A mental health professional can help you understand what is contributing to your stress and develop practical ways to manage it.
Depending on what you are experiencing, this may include:
- Evidence-based psychological therapies
- Support with anxiety or low mood
- Developing healthier coping strategies
- Learning relaxation and emotional-regulation techniques
- Processing difficult or traumatic experiences
- Making changes to patterns that may be contributing to ongoing stress
Understanding the HPA axis can help explain why stress feels so physical.
Stress is not simply something that happens “in your head”. It involves a coordinated response across the brain, nervous system and body.
And when that response remains activated for too long, recognising the signs and getting the right support can make a real difference.
