Final answer:
The hygiene hypothesis proposes that the decrease in infectious diseases and increase in cleanliness have led to an increase in allergies, asthma, and autoimmune diseases. Without infectious diseases to fight off, the immune system may start attacking the body's own cells, leading to autoimmune diseases. Additionally, the immune system may overreact to harmless antigens, leading to allergies like asthma.
Step-by-step explanation:
The hygiene hypothesis explains the inverse relationship between infections, asthma, allergies, and autoimmune diseases. According to this hypothesis, the decrease in infectious diseases in developed countries and the emphasis on cleanliness have led to an increase in allergies and autoimmune diseases. The immune system, without infectious diseases to fight off, may start attacking the body's own cells, leading to autoimmune diseases. Additionally, the immune system may overreact to harmless antigens, leading to allergies like asthma.