Although antibiotic soap sounds safe, can you get too clean for your own good? At the risk of offending the "wash your hands before dinner" school of parenting, let's ogle a new explanation for asthma and allergy -- the "hygiene hypothesis."

According to this notion, early exposure to dirt, grit and infection seems to "tune" the immune system, preventing it later in life from getting worked up over harmless stuff like pollen or cat dandruff.

Future Why-Filer Pam Jackson gets mud behind her ears in an effort to reduce her future risk of asthma.
Courtesy Pamela Jackson.

The hypothesis gets some support from new research correlating low rates of asthma to exposure to dirt and infection in early childhood.

Oh, yes, and you can leave those antibiotics at the chemist's: There is also evidence linking childhood asthma with a history of taking these bacteria-killing drugs.

Asthma is an airway inflammation with complex environmental and genetic causes. In most cases, a hyperactive immune response -- an allergy -- plays a role.

Asthma closes the airways, making it tough to breathe. Many of the relatively new treatments can quiet the inflammation, keeping the airways open.

Let's forget treatment and stick with causes. Why did the asthma rate double in the United States between 1980 and 1996? Air pollution and tobacco smoke are prime candidates, but since they have not changed so much in 16 years, other causes beg for discovery.

Got evidence?
Into the breach rushes the hygiene hypothesis, which notes that people evolved with dirt, dust, grud and grime, and we (especially some boys we could mention) have no problem surviving such circumstances.

Can you be too clean?
Centers for Disease Control.

One who thinks the hypothesis is worth consideration is T.V. Rajan, head of the department of pathology at the University of Connecticut Health Center. "I have the view that we are basically ecosystems," he says, "and that we respond to all sorts of changes in the ecosystem."

For children who are brought up in sterile conditions, he adds, "there are consequences to that." Consequences, perhaps, but evidence? Yes, there is some, and while it's fascinating, it's also suggestive, not conclusive.

Researchers have found that younger siblings in large families have fewer allergies. (Don't believe us? Then read more). The phenomenon was particularly pronounced if the older sib was a boy (so mucky guys actually help bring home the dirt, not the bacon).

Exposure to farm-raised milk and stables reduced the incidence of asthma and hay fever in Austrian children. Only 1 percent of children who had been in barns and drank farm milk had asthma, compared to 11 percent of city-slicking kids (see "Exposure to Farming..." in the bibliography).

Kids who got no antibiotics early in life have fewer allergies, according to a study published in 2000. Belgian kids who'd taken antibiotics had 1.7 times the risk of asthma and 2.3 times the risk of hay fever compared to kids who had not taken them. See "Does the Use of Antibiotics... " in the bibliography.

What we're talking about is a new way to see the world, or at least the dirt. Why would anyone even propose such a heretical notion? Rajan says he got interested in the hypothesis while studying the parasite filiarisis, which causes elephantiasis. He wondered why the immune system fights the parasite without eliminating it. The answer, he decided, was that the immune system was keeping enough antigen around to keep itself "primed" against further attacks by the parasite. "The immune system down-regulates itself before every last vestige of the infection has been eliminated," he says.

In hyper-clean conditions, the immune system lacks this downregulation, he suspects, and "it reacts dramatically to something relatively innocuous like pollen, because it has not learned to fine-tune itself."

Asthma records from United States, National Health Interview Survey, 1980-1994.
Morbidity and Mortality Weekly Report.

The data, please
It's heretical, the idea that a bit of infection could be helpful, but Rajan is not alone in suspecting that cleaning up our act could backfire. Yet the evidence for the hygiene hypothesis is circumstantial, and even Rajan describes it as "not convincing."

The debate matters because asthma is exploding. According to the Department of Health and Human Services, the number of patients doubled between 1980 and 1996, by which time 14.6 million people had the disease. The rise was quickest among children under five years -- 160 percent between 1980 and 1994. Asthma is also abnormally common among low-income people and minorities.

In 1996, asthma caused:

9 million doctor visits

1.8 million emergency room visits

460,000 hospitalizations and

5,000+ deaths

The idea is that challenging the immune system -- having it do its thing -- somehow balances it out, thus reducing not just asthma, but also inflammatory bowel disease and a bunch of other strange illnesses. The dirt 'n bug challenges, apparently, train the immune system much as Larry Dodder trains on a Dim-bus 2k before a quick game of quidditch.

Still, this is cutting edge stuff, perhaps better accepted among journalists than scientific types. Let's be realistic. While asthma is going up, dirt is going down. And correlation is not proof: the alarm clock rings in the morning, but it does not cause the sun to rise -- they just occur simultaneously.

So before you pitch the antibiotics and send your kids groveling around in the dirt, let's listen to a voice of caution. The hygiene hypothesis "makes a great deal of sense," says Rajan, 'but let's not confuse plausibility with reality. There are any number of theories that are plausible, but wrong. It's legitimate for the scientific community to be skeptical."

Grovel in the grut. Wade in the water. If you're really lucky, you might find a salamander.