It sounds like a contradiction. But some of the same worms we work hard to avoid are being studied — carefully, in labs — as possible treatments for stubborn immune diseases. Here's the honest version.
For almost all of human history, our bodies grew up alongside a crowd of microbes and parasites. Our immune systems learned to work with that constant company. Then, over the last century, clean water, sanitation, and modern medicine stripped most of it away — a huge win for health, and the right trade to make.
But some researchers noticed something odd: as parasites and infections dropped in wealthy countries, allergies and autoimmune diseases climbed. The "old friends" or "hygiene" hypothesis suggests our immune systems, with far less to do, sometimes start overreacting — to pollen, to food, or even to our own tissue. It is taken seriously, but it is genuinely contested: a 2016 review in PLOS Neglected Tropical Diseases notes that studies show contradictory results, and that part of the hypothesis rests on an erroneous assumption — that helminth infections have largely disappeared in high-income countries. They have not; the same review notes they remain widespread in the United States, including among the populations most at risk of inflammatory and autoimmune disease.
That idea led to a genuinely surprising line of research: what if deliberately introducing a mild, controlled worm infection could calm an overactive immune system? This is called helminthic therapy, usually studied with hookworm (Necator americanus) or pig whipworm.
It's been explored for conditions where the immune system attacks the body or overreacts, including:
In some studies, people living in areas where hookworm is common show lower rates of certain allergies — one of the clues that got scientists curious in the first place.
Worms have spent millions of years learning to survive inside a host without being thrown out. To do that, they quietly turn down the immune system's aggression. Researchers think that same calming effect is what might, in the right cases, ease an immune system that's stuck in overdrive.
Because the idea spread online, some people have tried to buy worms and infect themselves. That's genuinely dangerous. Real parasitic infections can cause anemia, malnutrition, serious complications, and harm to others — and what you'd buy online is unregulated and unsafe. The controlled dose used in a study is nothing like swallowing something from the internet.
The takeaway isn't "go get a worm." It's something gentler and more interesting: not every parasite is a monster, and our relationship with them is more complicated than fear alone. That's the whole spirit of this site.
Not every worm is a villain.
Is It a Parasite? — four pages, plain English, from CDC and WHO sources. The red flags and a printable prevention checklist.
