(RxWiki News) The joke is that experienced parents don't clean off a pacifier after it falls on the floor. A few extra germs just build the immune system, right? Well, they may be on to something.
Scientists and parents have long thought that too much hygiene and cleanliness may be contributing to allergies and certain chronic conditions like asthma.
A new study reveals the first substantial scientific evidence to support the idea that exposing your kids to too few germs when they're young may actually hurt them in the long run.
"Encourage your children to play outside and explore."
Lead author Torsten Olszak, MD, a research fellow at the Brigham and Women's Hospital at Harvard Medical School, and colleagues explored possible evidence for the "hygiene hypothesis" in a recent study with mice.
The researchers studied the immune systems of two types of mice: "germ-free" mice who were not exposed to bacteria or other microbes, and normal mice in a normal environment.
Ozszak's team found that the T cells of the germ-free mice were hyperactive. T cells are one type of immune cell that helps build the antibodies to fight disease, but they have also been associated with autoimmune disease, or illnesses that directly affect the immune system, such as asthma, lupus or inflammatory bowel disease.
In fact, the mice without exposure to microbes had greater inflammation in their lungs and in their colons, which looked similar to the way asthma affects the lungs and colitis affects the bowels.
When the researchers exposed some of the germ-free mice to bacteria in their first few weeks after birth, but then denied them exposure after that, those germ-free mice ended up with normal immune systems with the typical ability to fight off disease - for the rest of their lives.
"These studies show the critical importance of proper immune conditioning by microbes during the earliest periods of life," said co-senior author Richard Blumberg, MD, chief for the Brigham and Women's Hospital Division of Gastroenterology, Hepatology and Endoscopy.
"Also, now knowing a potential mechanism will allow scientists to potentially identify the microbial factors important in determining protection from allergic and autoimmune diseases later in life," Blumberg said.
Because the study was conducted in mice, however, the findings cannot be completely extended to humans yet. The type of research done in this study with mice would be impossible or unethical in humans.
However, further studies of different kinds can provide researchers with more information on how much the hygiene hypothesis might explain the increase in various autoimmune diseases and conditions like asthma.
The study appeared online March 22 in the journal Science. The research was funded by the National Institutes of Health, Crohns Colitis Foundation of America, Harvard Digestive Diseases Center, Medizinausschuss Schleswig-Holstein, and Deutsche Forschungsgemeinschaft. No conflicts of interest were noted.