It's allergy season and it's hitting some of us especially hard. Why? One theory suggests it's because we live in cities and not in the country as nature expected.

Allergist Dr. Dat Tran at Houston's UT Health Science Center says the immune system is designed to stop bacterial infections. But when city hygiene keeps it from encountering that bacteria...

"Then the immune system starts to react to other components in the environment that it shouldn't react to."

Dr. Tran says farmers don't usually have this problem.

"People who live on farms; who are with animals and play in the dirt -- they have less development of allergy."

Dr. Tran says it's also true some of us are more genetically disposed to suffer from allergies. He says some of us are born without a gene that helps the skin resist allergens and bacteria.