What are the factors responsible for causing diseases?

Causes of diseases: These include the factors or agents that are responsible for causing a particular disease. The factors responsible for causing diseases may be external or internal factors.

1. Extrinsic or external factors :

• The disease-causing external agents such as bacteria, viruses, and pollutants that enter the body from outside the body, are referred to as external factors.
• The external factors include pathogens, environmental pollutants, and intake of tobacco, drugs that lead to various diseases such as common cold, influenza, chickenpox, rabies, typhoid, asthma, respiratory illness, lung cancer, night blindness, marasmus, diabetes, heart diseases, etc.

2. Intrinsic or internal factors :

• The disease-causing factor that exists within the body of a person is referred to as an intrinsic factor.
• The internal factors include genetic defects, hormonal imbalance, improper functioning of parts of the body, and malfunctioning of the immune system which becomes the reason for various diseases such as Grave's disease, heart failure, cataract, kidney failure, hemophilia, sickle cell anemia, dwarfism, cancer, asthma, etc.