Today, there are so many health problems known to humans, ranging from common cold to heart failures, and from diabetes to cancer. During ancient days, people believed these health problems and sickness as the result of God’s anger or the act of evil spirit.
Later, Hippocrates and Galen studied the causes and explained that the sickness is caused by the imbalances of four substances in our body. These four substances that they identified were – blood, phlegm, black bile, and yellow bile. As the studies advanced, Paracelsus found that the sicknesses are caused from outside forces too.
The advancement in medical studies categorized diseases into two categories – infectious and non-infectious. Infectious diseases are caused by viruses, fungi, parasites, and bacteria. These four causes are known as pathogens.
Non-infectious diseases are caused by many different factors including our life style, living environment, genetics, etc.