About 25 years ago, a British researcher noted that younger children in large families seemed to have fewer allergies than older siblings. The researcher suggested that younger siblings may develop protection from allergies because they’re exposed to a variety of germs early in life, thanks to their older siblings.
Around the same time, doctors in many Western countries were noting a huge upswing of allergies. Many wondered if smaller families and cleaner living conditions — less exposure to various microbes early in life — could be behind the surge. “Why do we have more allergies and autoimmune disease now?” asks Maria I. Garcia Lloret, MD, assistant clinical professor of allergy and immunology at UCLA. “What is it about us? Is it that we are too clean?”
The answer may be yes. The so-called “hygiene hypothesis” has gained credence and has evolved into an even more sophisticated understanding of the “microbiome,” or the diversity of microbes that surround us, permeate our bodies and influence our health. Sophisticated tools to look at the genetic signatures of various microorganisms now suggest that we are awash in microbes. While some are harmful, others support normal bodily functions.
“Microbes on our skin and in our guts rule a lot of what happens to us, aside from causing infection,” Dr. Garcia Lloret explains. “The microbial diversity contributes to our health. Therefore, if you disrupt the microbial environment, you are interfering with the good things that are able to control the allergic response.”
Now doctors think that babies and young children who live in very clean environments may be more likely to develop allergies, allergic skin conditions and inflammatory bowel disorders. “The less diverse your microbes are, the more prone you are to diseases like inflammatory bowel disease and allergies,” Dr. Garcia Lloret says. “The new understanding is that we require microbial diversity to thrive.”
However, the hygiene hypothesis still has not yielded much practical advice, says UCLA pediatric pulmonologist Sande O. Okelo, MD, PhD. “I don’t think the evidence is there yet that would allow physicians to start prescribing any particular type of therapy relative to the hygiene hypothesis,” he says.
The one exception is the use of probiotics to reduce the incidence of eczema in babies at high risk for allergies. Recently, the World Allergy Organization issued guidelines stating that pregnant women with allergies or asthma can consider taking probiotics — live microbes that can be formulated into many different types of products, including foods, drugs and dietary supplements — in the second half of pregnancy. The guidelines also recommend breast feeding infants that are at high risk for allergies — those with a parent or sibling with an allergy have a 20-to-30 percent risk of also having an allergy — and giving them probiotics.
Further advice for consumers awaits more study. But, says Dr. Okelo: “The hygiene hypothesis is definitely worth exploring because prevention is the ultimate medicine.”