The idea of having parasitic worms is pretty disgusting. But scientists are increasingly realising that some of these worms do us more good than harm.
Some have gone so far as to introduce certain parasites into people's systems.
Immunologist Joel Weinstock of Tufts University in Boston says the medical profession has spent years trying to work out what was causing people to suffer from inflammatory bowel disease like Crohns.
He wondered if the issue was in fact caused by the lack of something in the gut, in particular certain parasites no longer found in western countries, where such immune conditions and allergies are far more common.
He talks to Jesse Mulligan.
