Of all the things young children put in their mouths, dirt may provoke the most concern among parents fearful that eating it will give kids worms.

Although there are reasons not to eat soil, worms may not be one of them.

Researchers have long been investigating the link between being too clean and failing immunity. Fecal material from healthy people has been shown to help fight antibiotic-resistant infections in patients for whom nothing else worked. Now, some scientists, private companies — and even Web-surfing patients — are looking into the potential health benefits of ingesting worms.

In the developed world, it’s been decades since intestinal worms were a familiar part of the human biome, the general term for all the organisms that thrive in people. But as worms have disappeared, rates of autoimmune and allergic diseases have skyrocketed. The correlation doesn’t necessarily mean causation, but it is getting more attention.

William Parker, associate professor of surgery at the Duke University Medical Center, said the worm-allergy connection “was published about 40 years ago.” The pioneering worm advocate, British scientist John Turton, had a hunch that intentionally inducing an immune response with human hookworm might quell his body’s internal war on pollen.

The human immune system evolved in the presence of these intestinal worms, known as helminths. Decades ago, human antibodies attacked the worms, keeping them at bay. But since the 1960s, when the Western world orchestrated a mass extinction of this worm population, those antibodies have sought a new target. For many, that’s meant an overreaction to pollen and even their own bodies, Parker said.

“As far as the big picture of human health goes, it’s pretty much already accepted that when you put helminths back into the ecosystem of the human body, you can resolve allergic and autoimmune diseases,” he said.

Helminthic therapy is done with worms at the tiny, larval stage, not the kind of long worms that populate parental nightmares. As human antibodies do their work, depending on the species, the worms die off before they can grow, or before they can proliferate.

Although the use of helminths in humans is not approved by the U.S. Food and Drug Administration (clinical trials are continuing), there are about 7,000 people in the world using helminths. Treating diseases that stem from chronic inflammation appears to hold the greatest promise.

Advocates stress that helminths must be carefully selected. Neilanjan Nandi, assistant professor of gastroenterology at the Drexel University College of Medicine, said, “Not all parasites are created equal.”