The connection between our emotional (psychological) health and physical health is very complex. Psychological stress can affect our health. Researchers know that stress, especially chronic stress, can weaken the immune system. The immune system defends our bodies against infections and diseases, such as cancer. A weakened (compromised) immune system plays a role in the development of some types of cancer. Stress can also alter the levels of certain hormones in the body.
Cancer is a complex disease. It develops from a combination of risk factors, including heredity, lifestyle and environmental factors. Stress can cause people to turn to unhealthy behaviours, such as overeating, smoking and heavy drinking, which may affect cancer risk.
Studies have looked at the relationship between psychological factors, including stress, and cancer risk, but there are conflicting results. Some studies suggest a link between various psychological factors and an increased risk of developing cancer. Most studies found that stress does not increase the risk of cancer. Research has not proven a definite cause-and-effect relationship between psychological stress and cancer development.
Scientists are also studying how stress can affect how a tumour grows and spreads (metastasizes). Some studies indicate that stress may affect how a cancer grows and spreads, but it is still not known exactly how it does this.