A non-communicable disease cannot be passed from one person to another. It is not caused by a pathogen such as a bacterium or a virus. Examples include cardiovascular disease, many forms of cancer, some lung diseases, some liver diseases, and diseases influenced by nutrition, such as type 2 diabetes.
Most of these diseases have more than one cause. Several factors interact, and the more risk factors a person has, the greater the chance of becoming ill. The factors include the genes a person inherits (a genetic risk), their lifestyle (diet, exercise, smoking and alcohol) and their environment (for example polluted air or contact with harmful chemicals). The disease is the result of the interaction of several factors, not of one factor on its own.
For example, a person with a family history of heart disease may inherit a higher risk, but eating a diet high in fat and taking little exercise makes the disease more likely. Smoking and air pollution can both damage the lungs, so living in a polluted city and smoking together raise the risk of lung disease. Poor nutrition can mean too much food, as in obesity, or too little or the wrong balance, as in malnutrition.