Health — Health is defined as a state of complete physical, mental and social well-being, and not merely an absence of disease or infirmity.
Disease — Any physical or functional change in the body from a normal state which causes discomfort or disability is called a disease.
Pathogen — Pathogens are disease-causing germs (microorganisms) that have the potential to cause infectious diseases. For example, viruses, bacteria, protozoans etc.
Allergen — Allergens are substances that can trigger an unpredictable allergic reaction in individuals.
Hygiene — Hygiene is defined as science and practice of maintaining good health.