How the mind and body interact to influence health has long been discussed. Although people speak casually about mind and body as though they were distinct, they are actually so interrelated that it is hard to separate their effects, as in the following cases:

• Social and mental stress can aggravate many physical disorders, including diabetes mellitus, coronary artery disease, and asthma.

• Stress and other mental processes can aggravate or prolong physical symptoms. For example, people who are depressed or anxious may suffer more if they become ill or injured than people who are in a better frame of mind.

• Stress sometimes can contribute to physical symptoms even when no physical disorder is present. For example, children may develop abdominal pain or nausea because they are anxious about going to school, or adults may develop a headache when they are under emotional stress.

• Thoughts and ideas can influence how a disorder progresses. For example, people with high blood pressure may deny that they have it or that it is serious. Denial may help reduce their anxiety, but it may also prevent them from following their treatment plan. For example, they may not take their prescribed drugs, thus worsening their disorder.

• A general physical disorder can influence or lead to a mental health problem. For example, people with a life-threatening, recurring, or chronic physical disorder may become depressed. The depression, in turn, may worsen the impact of the physical disorder.

• A physical disorder of the brain, such as Alzheimer disease, can affect someone's personality and/or ability to think clearly.

When physical symptoms result from stress or mental factors, doctors may have difficulty identifying the cause. Various diagnostic tests may be required to clarify the situation.