Disease results when the Qi of the body is weakened and unable to resist the onslaught of pathogens (disease-causing factors). In Chinese medicine the agents that cause disease are given the name of meteorological conditions; an infection (often associated with a fever) is called a disease of heat, and a chronically painful joint is usually a disease of cold. These pathogens allow diseases to be grouped according to their broad symptoms. The pathogen wind is an interesting idea. Wind means a changeable symptom, so the type of muscular ache often occurring with 'flu, would be classed as invasion by wind. The idea that disease is due to physical conditions is an intuitive explanation for many common aches and pains. People often complain that 'the caught a chill when they got wet', or that their 'neck is stiff after having slept in a draught'. The Chinese pathogens represent formalization of this approach.

A particular pathogen usually presents itself with a defined symptom complex. By using the information gained from the history of the disease, and the physical examination of the patient, it is often possible to make a clear diagnosis of the pathogen causing the disease. If the patient has a fever then heat is one of the pathogens involved in the disease process. Once the diagnosis has been made, then specific acupuncture points can be used to disperse the pathogen; when heat is the invading pathogen, then specific points are used to reduce the fever. Acupuncture points are therefore used to correct the Yin Yang balance of the body and to disperse pathogens.

If the pathogen cold is responsible for a particular disease process, then heat must be used to treat it. Moxa is the Chinese version of the heat lamp and, as shall be discussed in a late chapter, the Chinese burn the dried leaves of Artemisia vulgaris over the areas that require heat. Heat, or more specifically smoldering moxa, provides local heat for a variety of chronic muscular aches. It is interesting to note that the types of disease due to cold are commonly the muscular and rheumatic ache which are temporarily alleviated by heat lamps.

More than one pathogen can invade at the same time; if a patient is suffering from 'flu, then there will be a fever and all muscular aches that wander all over the body. This is defined as invasion by the pathogens wind and heat and, as one doctor said when I described this to him, 'the patient will be suffering from a great deal of hot air.'

Other factors may also cause disease, such as worry, or eating contaminated food. The Nei Ching Su Wen states that excessive grief, anxiety and overthinking will cause cancer. This idea has been supported by some recent comments in the medical press which suggest that if a woman has a breast removed for cancer she will survive longer if she is of a 'happy' disposition.