The factors which affect health of human can be divided into two groups – intrinsic factors and extrinsic factors. Intrinsic means internal and extrinsic means external.

1. Intrinsic factors – Those diseases-causing factors which exist within the body are called intrinsic factors. There are several important factors which affects our health are

• Hormonal disease – These diseases which are caused by a defect in the production of hormones or action of hormones in our body are called hormonal disease. Hormones are protein which control many parts of human’s body processes which are related to the normal development and health growth. Deficiency of hormones in the body causes diseases and excess of hormones also causes diseases. The important hormonal diseases are Cretinism, Diabetes, Dwarfism and Gigantism.
• Genetic diseases – These types of diseases which are transferred from generation to generation are called genetic diseases or generally transmitted diseases. There are important genetic diseases are Sickle cell anemia and Haemophilia.
• Improper functioning of body organs – There are several diseases are caused by malfunctioning of body parts such as kidney failure(improper functioning of kidney), cataract and myopia(improper functioning of eye-lens), cardiac failure (improper functioning of heart), and Osteoporosis(malformation of bones).
• Malfunctioning of immune system of body (or Allergy) – The sensitivity of a person to certain substances such as pollens, dust, certain foods like egg and fish, serum, and certain drugs or fabrics is called allergy. Allergy occurs due to the malfunctioning of the immune system of the body of the person concerned. It can be prevented by avoiding the allergic causing substance.

2. Extrinsic Factors – The disease-causing which come from outside the human body are called extrinsic factors. There are several important extrinsic factors which affect or harm our health such as

• Nutritional disease – A disease caused by a deficiency of essential nutrients such as fats, proteins, carbohydrates, minerals and vitamins in the diet or food is called a nutritional disease.
• Disease caused my micro-organisms – There are several disease caused by micro-organisms (viruses, protozoa, bacteria and fungi) enter into the human body through impure or infected water, air and food and also insect bites such as tetanus, cholera, food poisoning, malaria and many more diseases.
• Environment pollution – There are several elements which pollute the environment such as carbon dioxide, dust, carbon monoxide, pollen, nitrogen oxides and sulphur dioxide. It causes several diseases such as cough, lung disorder, headache, and bronchitis. Some pesticides and chemical wastes can also harm the health of human