Is Hygiene Theory Responsible for the Rise in Allergies?

Sanitation has been improving for hundreds of years. So why are we seeing such a big pickup now in the past 20 to 30 years? That's not entirely clear. For something like allergies, it's pretty likely that there are multiple factors at work here. Even if the hygiene hypothesis seems to be the strongest theory, there might be some other element playing a role here as well.