What causes infectious diseases?

Answer 1

Poor sanitation, lack of hygiene, and bad diets.

Answer 2

An infectious disease is caused by a microorganism entering and attacking your body. People can pass these microorganisms from one person to another. This is called infectious.
An infectious disease is transmitted from some source. Defining the means of transmission plays an important part in understanding the Biology of an infectious agent, and in addressing the disease it causes. Transmission may occur through several different mechanisms. Respiratory diseases and meningitis are commonly acquired by contact with aerosolized droplets, spread by sneezing, coughing, talking, kissing or even singing. Gastrointestinal diseases are often acquired by ingesting contaminated food and water. Sexually transmitted diseases are acquired through contact with bodily fluids, generally as a result of sexual activity. Some infectious agents may be spread as a result of contact with a contaminated, inanimate object (known as a fomite), such as a coin passed from one person to another, while other diseases penetrate the skin directly.

Answer 3

smoking and body pressure