My sister works as a physician at Phoenix Children’s Hospital and they are literally studying whether giving “dirt pills” to children helps prevent asthma. Wish I could find the link for more info.

Coronado Biosciences tried to treat Crohn's disease using hookworm eggs. Basically give the patient a bunch of eggs, the hook worms hatch, cause an immune response, then die (as they can’t live in humans).

Clinical trial showed no impact at all on the disease.

A great idea for a startup.

Because it's easier and more effect for one to just go outside.