ALLERGIES AND ASTHMA: Rooted in Excessive ‘Cleanliness’?
Responding to the recent rise in allergies and asthma cases in developed nations, some scientists are arguing that living in cities, insulated from nature, has left many people susceptible to allergies, asthma, certain autoimmune diseases and possibly diabetes, USA Today reports. The so-called "hygiene hypothesis" holds that good hygiene leaves the body's immune system underdeveloped and vulnerable to pollen, animal dander and other ordinarily harmless substances. "The immune system learns from experience. If it doesn't get the right kind of practice, it develops imperfectly," Irun Cohen, an immunologist at the Weizmann Institute of Science in Israel, said. According to a recent CDC study, asthma rates in the United States have increased by 75% since 1980, growing by as much as 160% in children. Although doctors suspect excessive cleanliness may have played a role in the increase, they do not recommend that people expose themselves or their children to germs. "We don't quite have the smoking gun, but we're close," Philippa Marrack of the National Jewish Medical and Research Center in Denver said.
Dust Bunny Cure?
According to a study by Marrack's colleague Andy Liu, exposure to endotoxin, a molecule in house dust, might offer the best protection against allergy or asthma. "Early childhood exposure to endotoxin may be the common thread in communities where asthma and allergies are uncommon," Liu, whose research was published in the May 11 issue of The Lancet, said. Liu's team studied the homes of 61 infants for the period between the ages of nine months and their second birthdays, testing them for sensitivity to dust mites, cats, dogs, cockroaches, mice, milk, eggs and soy, as well as the endotoxin concentrations in each house. Of the children, 51 tested negatively for sensitivity to those allergens; these children also had the highest concentration of endotoxin in their homes. "The study supports the thesis that exposure to endotoxin early on has an impact on the subsequent development of the immune system," NIH parasitologist David Sacks explained. Marrack warns, however, that scientists must conduct more studies to confirm the hypothesis.
Better Safe Than Sorry
While some scientists also have advocated theories that immune deprivation may lead to autoimmune diseases such as multiple sclerosis or diabetes, others note that today's children from higher-income families contract far fewer serious infections -- such as plague, cholera, typhoid fever, diphtheria, polio and small pox -- than in the past. "What we're seeing now [with rising allergy and asthma cases] may be a consequence of being too protective ... [b]ut being protective has kept a lot of children alive," Marrack said (Sternberg, 7/6).