If your doctor told you that you were infected with worms, your first question would probably be, “How quickly can I get rid those worms in me?” And I get that.

I mean, look, you don’t want worms wriggling around inside your intestines.. It’s enough to gross anybody out.

But what if I told you that you might want to have parasitic worms inside you? Because some doctors have actually found a connection between having worms and not having immune system problems like allergies or arthritis. The idea is that these worms have set up shop in our bodies for so long, evolutionarily speaking, that our immune systems might have gotten used to them — to the point that being worm-free can actually cause its own issues.

It’s part of the hygiene hypothesis, which was proposed by epidemiologists back in the 1980s to explain why allergies and autoimmune conditions like asthma are so much more common today than they used to be. According to the hypothesis, people’s immune systems might be out of whack because we’re too clean. Filtered water didn’t exist for an awful long time, let alone hand sanitizer stations..

So for much of our evolutionary history, everyone was constantly exposed to things like bacteria and parasites. It’s your immune system’s job to keep these things from settling in and harming you when they get inside. So when it finds something foreign, it defends your body by triggering inflammation — that hot, red, swollen achiness.

Those symptoms happen because the area is flooded with an army of white blood cells. The compounds they release either attack the foreign material, or call in reinforcements. But the compounds that do the bulk of the attack don’t just target invaders..

They can harm your own cells, too, and your body can get caught in the crossfire, which causes damage and pain. Allergies, for example are a special case of inflammation, where the body is overreacting to something that’s usually harmless, like pollen or dust. And autoimmune disorders come from parts of your own body triggering inflammation.

Like rheumatoid arthritis, where joints basically become permanently inflamed, or multiple sclerosis, where the immune system attacks the protective coating around nerves, and sometimes the nerves themselves. All these conditions are becoming more common these days, especially in wealthy nations where you would think easy access to high-quality medical care would prevent them.. That’s where parasitic worms, collectively known as helminths, come in.

The group includes things like tapeworms, nematodes, and flukes, which steal nutrients to survive. Most get cozy in another animal’s intestines or blood. Some species cause pretty severe symptoms—like the worms behind schistosomiasis, which can cause anemia, liver failure, bladder cancer, or other awful conditions.

But many others don’t.. Like, if you had a tapeworm right now, you might have no idea. Which is a super creepy thought, actually.

For those more benign species, the fallout that can come from launching your immune system nukes at them can be worse than the damage from the worms themselves. Which is why some epidemiologists think that our immune systems have evolved to function with certain parasites, to some extent.. That might sound kind of backwards, but studies have found that rates of asthma and allergies are higher in places with fewer parasite infections, like those with more sanitation and access to healthcare.

And even though treatment is obviously worth it when the worms are causing health problems, other research has suggested that getting rid of parasites can have unintended side effects. For instance, in a 2006 study, ridding 317 children from Gabon of their intestinal parasites made some of them have an allergic reaction to mites. Similarly, a 2011 study looked at more than 2500 Ugandan women, some of whom were treated with de-worming meds while they were pregnant..

While the treatment helped prevent potentially serious complications in both adults and babies, it increased the likelihood that the kids would have eczema or wheezing—both symptoms of allergic responses. And a small study of 12 multiple sclerosis patients found that those with worms had less nerve damage over time. But when 4 of them were treated, their multiple sclerosis symptoms got worse.

It seems strange that having a parasite infection could keep you healthier in these specific ways. So to figure out why this pattern exists, immunologists have looked at how our bodies respond to helminth infections. They’ve found that some parasitic worms seem to make our immune systems kind of hold back by releasing anti-inflammatory signals that make it so our bodies don’t go overboard trying to kill the parasites.

At the same time, they’re also reducing the inflammation that leads to autoimmune conditions, and the overreaction to allergens.. Helminths could also spur the production of regulatory T cells, which recognize parts of your body that might trigger inflammation and turn down the response. These cells normally keep your immune system from staying in attack mode after the invaders are already dead, or from freaking out in response to harmless stuff like pollen.

And this was seen in those 12 multiple sclerosis patients—those with parasites had more regulatory T cells recognizing a protein that triggers the attack of neural tissue. Which could be why they had less nerve damage. Doctors are trying to figure out what it is about the worms that triggers these regulatory mechanisms.

That way, they might be able to turn the compounds involved into treatments for all kinds of autoimmune diseases. It would be all the benefits of worms, without the worms!. To be clear, we here at SciShow do not recommend infecting yourself with worms to try and, like, cure your tree nut allergy.

Unless your doctor prescribes them, which is … kind of possible. Some doctors are putting the hygiene hypothesis to the ultimate medical test: clinical trials. Most of these trials are still in the early stages, and results are mixed..

But some researchers remain hopeful. We already know that our health depends on tons of other organisms that live on and in our bodies. So maybe parasitic worms are just part of that.

Just a lot bigger. But again, we are not recommending that you stop washing your hands or, like, walk around barefoot around a lot of human feces. Don’t do that..

If you want to learn more about your health and medicine and healthcare policy you can dive even deeper by checking out our sister channel Healthcare Triage hosted by Dr. Aaron Carroll over at youtube.com/healthcaretriage..