The hygiene hypothesis does include that, but also includes exposing yourself to more antegens helps prime the immune system better. bum worms can evade the immune system by in capsilating themselves and so remain outside the target zone. They inhibit or down regulate the host immune system which dampens the immune system from hyper active disorders like asmurinnd and so forth. In saying that, they've now shown that it does increase the risk of other infections like tuberculosis and hi-virus.