Allergy & Air on May 20, 2015 0 Comments If you are normally obsessed with housekeeping, the Hygiene Hypothesis is like a free pass to give up your obsession—guilt-free! On the other hand, if dusting and vacuuming don’t float your boat, so to speak, then the Hygiene Hypothesis may give you carte blanche to continue life among the dust bunnies—and still feeling happy that you’re not running the risk of asthma and allergies. So what is this “Hygiene Hypothesis” and why is it challenging the long-held notion that cleanliness is next to godliness? Is it true that your house doesn’t have to be spic-and-span for your family to avoid respiratory distress? The Hygiene Hypothesis The Hygiene Hypothesis was proposed in 1989 by David P. Strachan, MD, PhD, of St. George’s University of London to explain an upward trend in allergies. The theory is that parents were making their children more vulnerable to allergies and asthma by cleaning their homes too well and by having smaller families. This meant a lot less opportunity for infants and developing children to be exposed to allergens and other natural “invaders” in the environment. Without such exposure, developing immune systems essentially could not recognize and catalogue the threats, and build a defense against them. The Hygiene Hypothesis also linked “too clean” homes to an increase in inflammatory bowel disease, but the precise scientific explanation remains largely a mystery. An immune system that is finely calibrated to the environmental conditions is able to identify real threats and respond appropriately—not overreact to things that pose no genuine threat. Chronically overreacting is a hallmark of asthma and allergies. The Asthma and Allergy Foundation of America says, “Everyone’s airways react to irritating substances. In asthma sufferers, the airways are always overreacting.” A research study involving mice seems to support the Hygiene Hypothesis. Mice that were raised under sterile conditions were more likely to develop a form of allergic asthma and also colitis, a bowel disorder. But the journal that published the research is quick to add that what’s true for mice may not be true for people—the pathways the human body uses to determine its response to “environmental invaders” are complex and not fully understood. The choices the body makes could also lead to disease of various kinds. Fundamentals of Asthma and Allergies To many folks, “allergies” means sneezing or hay fever and “asthma” is labored breathing and wheezing. Those definitions are true, but they don’t go quite far enough. An allergy is an inflammatory reaction to a specific substance that can involve the nose, eyes, skin, tongue and breathing passages; asthma is a chronic inflammatory disease of the lower respiratory system and can be very serious, especially for children. Allergies and asthma can have the same triggers. Children and adults can have allergies without asthma, but typically people with asthma also have allergies. Common triggers are allergens (dust mites, mold, pollen, animal dander and cockroach debris), cold air, exercise, cigarette smoke, viruses and components of bacteria and fungi. Luckily, there are air purifiers that could possibly lessen the severity of your asthma. The Hygiene Hypothesis addresses only the first type of asthma below. Four Kinds of Asthma 1. Allergic Asthma, Atopic Asthma, Extrinsic Asthma Whichever name you use, this is the most common form of asthma, found among more than half of the U.S. children and adults who have asthma, and it’s the kind addressed by the Hygiene Hypothesis. When the body is exposed to certain irritants, like animal dander or dust, it reacts with an antibody called Immunoglobulin E (IgE). IgE binds with mast cells that can cause inflammation and a cascade of allergy symptoms occur. There is a tendency for this type of asthma/allergy to run in families. 2. Intrinsic Asthma This type of asthma frequently develops among individuals who have recurrent infections of the sinuses, bronchi, tonsils and adenoids. It occurs when an adult or child is particularly hypersensitive to the bacteria or viruses causing the infection. Triggers of these asthma attacks include infections, stress and other high emotions and irritants. 3. Mixed This type is a combination of extrinsic and intrinsic asthma. 4. Bronchial Asthma An individual who has recurrent attacks of breathlessness, wheezing and tightening of the bronchial tubes can develop this kind of asthma. The severity of attacks has a wide range, from mild with some wheezing to near-suffocation. Extrinsic (“Atopic”) Asthma and the Hygiene Hypothesis: Research Primary “invaders” that can trigger atopic asthma and allergy attacks are: Dust mites, mold, animal dander, cockroach debris and environmental toxins Endotoxins (substances found in the cell walls of bacteria) Beta glucan (substances found in the cell walls of fungi) Viruses that cause respiratory disease, particularly respiratory syncytial virus (RSV) and parainfluenza virus Let’s look at what recent research has to say about each: Dust mites, mold, animal dander, etc. We spend 90 percent of our lives indoors, so the amount of dust, mold and pet hair in our indoor environment is no small matter. Research published in the Journal of Asthma in 2012 (PDF) summarized what many studies have shown: The prevalence of asthma appears greater among children and adults who are repeatedly exposed to dust mites to the point of triggering an immune response The development of asthma follows exposure to allergens in early childhood Strictly avoiding exposure to dust mites reverses asthma symptoms When children are exposed to dust mites more often, their symptoms worsen Outdoor allergies, such as reactions to pollen that we typically refer to as hay fever, don’t develop until a child is a little older (4 or 5) after enough exposure to develop sensitivity. Endotoxins Endotoxins, we know, are parts of the cell wall of bacteria. They are more baffling and confounding when it comes to asthma. Children raised on farms with greater exposure to animals and endotoxins have less atopic asthma and allergies. Researchers believe the endotoxins must offer some sort of protective effect, but they’re not sure how or why. It could have something to do with triggering a certain “switch” in the immune system, called TLR4, but researchers have cautioned against drawing the easy conclusion that “dirt is good.” There may be something else about a farm environment that protects against these respiratory conditions. They just don’t know for sure. Plus, even if endotoxins protect against asthma and allergies, they may promote infection. Exposure to endotoxins in adults presents another wrinkle. The most common form of asthma treatment—corticosteroid medication—is less effective in adults who have higher exposure to endotoxins. This study argues for a cleaner indoor environment, in opposition to the Hygiene Hypothesis. Beta glucan Another study shows that children exposed to beta-glucan dust (found in the cell walls of fungi) between the ages of 7 and 10 are more likely to have persistent atopic asthma four years later than children who have not had this exposure. And again, once a child has developed asthma, being further exposed to beta-glucan significantly worsens their condition; for each unit of beta-glucan, the likelihood of hyperresponsive bronchi nearly doubles. Virus Two viruses in childhood that can lead to asthma later in life are respiratory syncytial virus (RSV) and parainfluenza virus. With exposure to these viruses, inflammation occurs in the bronchi (bronchitis) or the lining inside the lungs (pneumonia). RSV appears to trigger the TLR4 “switch” mentioned earlier. On one hand, this switch may help the child’s immune system adapt to “invaders” in the environment. On the other hand, the U.S. Food and Drug Administration says it’s not that simple. With these viruses, the switch can be flipped in a variety of ways—not all of them beneficial. The Bottom Line In weighing the evidence for and against the Hygiene Hypothesis, the venerable institution, the Mayo Clinic warns against oversimplification: “Preventing asthma isn’t as simple as avoiding antibacterial soap, having a big family or spending time on the farm.” Viruses cause asthma rather than prevent it. Infections that seem “asthma-protective” can lead to worse problems. Once diagnosed, asthma worsens with more exposure to allergens. Promoting exposure to indoor invaders is “likely to do more harm than good,” Mayo Clinic experts conclude. So get a “clean-house habit” or keep the one you’ve got.
