What Is the Hygiene Hypothesis

What is the hygiene hypothesis?

A) People who have more exposure to infectious agents will have an overactive immune system.
B) People who have less exposure to infectious agents will have an overactive immune system.
C) People who have better hygiene and are cleaner will have a weaker immune system.
D) People who have better hygiene and are cleaner will have more infections.
E) People who have better hygiene and are cleaner will have fewer infections.