What Is Psychoneuroimmunology?

Psychoneuroimmunology is a multidisciplinary area of research that brings together people working in different fields so that they can pool knowledge and explore research questions across traditional subject boundaries. It incorporates fields that have traditionally been separate, such as:

• neuroscience (which considers the function and disorders of the nervous system, including the brain),
• physiology (which considers how living organisms or parts of the body function when they are working normally),
• immunology (which considers the function and disorders of the immune system),
• genetics (which studies genes, how traits are inherited, and genetic variation), and
• psychosocial disciplines (which consider how psychological factors and the surrounding social environment influence how people function and behave).

How Does Psychoneuroimmunology Link Different Fields of Research?

Psychoneuroimmunology brings people like clinicians and healthcare practitioners, epidemiologists (researchers who study the causes, effects, and patterns of disease in groups of people), basic scientists (researchers who seek to improve our understanding of the world and how things work), and statisticians (researchers who compile and use statistical data to solve problems) together, to study how processes that influence our minds and thoughts interact with the body’s immune and nervous systems.

This can involve looking at how the nervous and immune systems function and their effects on people’s behavior when they are well or unwell, such as when disorders such as autoimmune diseases (which develop when the body’s immune system mistakenly starts to recognize the body’s own tissue as foreign and attacks it) and immune deficiencies (which occur when the immune system becomes weakened, potentially enabling problems like infections to occur more easily) develop. There is now good evidence that psychosocial stresses and interventions can affect our immune systems in ways that lead to changes in our health.

Although further research is needed, it seems that stressful events can trigger physical and cognitive (thought-based) responses that induce changes in the body that weaken or damage the immune system, by altering the way the endocrine system (a network of organs and glands that uses hormones to control processes in the body) and the sympathetic nervous system (the part of the nervous system that is responsible for the “flight-or-flight” response to things that we perceive to be threatening or harmful) work.

For example, environmental and psychosocial factors can influence the development of cancer and autoimmune diseases, and affect the speed at which we heal. It has also been shown that regular physical activity has an immunoregulatory effect, as well as improving symptoms of depression and low mood, and having positive effects on the heart and muscle fitness.

What Is the Skin–Brain Axis?

The skin–brain axis is the term given to the connections between the brain and the skin, and the ways that they communicate with each other. The skin is the body’s largest organ and has a number of functions. It cover’s the body’s entire surface and acts as a barrier to things like UV light, chemicals, and microbes that have the potential to make us ill like bacteria, and helps to regulate our body temperature.

The skin also plays a key role in sensing changes in our environment, and environmental changes that it senses are translated into chemical and biological messengers that travel via hormones, or the immune or nervous system, to reach the brain and other organs. For example, if you put your hand on something that is very hot, the skin on your hand sends signals via nerves to the brain that are translated as pain so that you move your hand away quickly, and the immune system is activated to repair any damage to your hand. Communication can also run from the brain to the skin.

Many skin conditions are linked with chronic stress, including eczema, psoriasis, and acne. Stress has also been shown to reduce the skin’s ability to act as a barrier, increasing the chance of infections. Sleep has also been shown to be important for the immune system to work effectively, and meditation has been shown to have positive effects on the mental health and immune system function in people with long COVID.

How Does Studying the Skin Help Research in Psychoneuroimmunology?

Studying the skin has several advantages for psychoneuroimmunology researchers. It is relatively easy for participants in research to give samples of skin and for them to be cultured in a laboratory. Skin swabs can be used to quickly and cheaply sample the populations of microbes (such as bacteria and viruses) that live on the skin’s surface when people have inflammatory skin diseases, and to investigate how they differ under non-stressed and stressed conditions.

Skin-related experimental models (these use systems, such as the culturing of cell in a laboratory, to investigate processes that are thought to be involved in diseases and to evaluate new drugs that are being developed) can also be used to investigate the influences of lifestyle, perception, and our behavior on how well our organs function. For example, it has been shown that the levels of stress that a person is experiencing around the time of being vaccinated against flu can predict how long lasting their antibody response will be against that flu strain in older adults.

It is also hoped that the study of skin diseases may improve our understanding of how inflammation in the different areas of the body affects the brain and, conversely, how inflammation and dysregulation in the brain and nervous system affects other areas of the body. Such research has the potential to increase our understanding of how trauma and disruptions to the immune system affect our mental health, and whether there are links between them and the development of neurodegenerative diseases such as dementia in later life.