Mention the diseases caused by external factors.

External factors: The disease-causing agents such as bacteria, viruses, and pollutants that enter the body from outside are referred to as external factors.

Diseases caused due to external factors :

1. Pathogens: Disease-causing microorganisms like bacteria, viruses, fungi, and protozoans transfer disease to the human body through contaminated food, water, physical contact, and sexual contact. Common diseases caused by pathogens are common cold, Influenza, Chickenpox, Rabies, Typhoid, and Ascariasis.
2. Unbalanced diet: The absence of nutritional food makes the person unhealthy but it also leads to deficiency diseases like Scurvy caused due to deficiency of Vitamin C, Night Blindness caused due deficiency of Vitamin A, and Marasmus is caused by deficiency of proteins in the diet.
3. Environmental pollutants: The pollutants which pollute the environment include oxides of nitrogen, sulfur, carbon, particulate matter, industrial chemical waste, and heavy metals like mercury, cadmium, lead, etc. These harmful pollutants cause harmful diseases to humans such as asthma, respiratory illness, lung cancer, etc.