Medical anthropologist Theresa MacPhail says allergic reactions — including everything from hay fever to eczema and asthma — are growing in the U.S. and around the world.

MacPhail is an associate professor of science and technology studies at Stevens Institute of Technology.

In her book: Allergic: Our Irritated Bodies in a Changing World, she explores several theories of why we are becoming more allergic to things, one of them being the theory that excessive emphasis on hygiene (and perhaps even showering) can contribute to the development of sensitivities.

"You've probably heard that we don't let kids eat enough dirt. They don't play in enough dirt. They're not around enough germs," she says. "We have seen that people who send their children to daycare centers, there's something about being in a daycare center that is also protective."

Lack of exposure to germs is making humans more susceptible to allergic reactions and weakening our immune systems. Kids need to get dirty, outside, they need to be exposed to dirt, it's pretty plain and simple.

here's a great explanation :

https://www.youtube.com/watch?v=X29lF43mUlo