Environmental factors in allergy: An argument against the hygiene hypothesis
Since 1989, allergists and clinicians have debated the “hygiene hypothesis,” in which researcher David Strachan proposed that improved hygiene in Western nations resulted in immunologic overreactions to substances that would otherwise not cause irritations as an explanation for increases in childhood allergy rates.
Under the hygiene hypothesis, the mechanism by which fewer infections would promote allergic reaction involves a lack of immunologic stimulation and an overcompensation in the form of traditional allergy symptoms such as sneezing, watery eyes and itching in response to potential allergens.
Ricardo Sorensen, MD, a pediatric immunologist at the Louisiana State University Health Sciences Center in New Orleans, leaves little doubt where he stands on this controversial issue. “I don't believe much of the hygiene hypothesis. The role of infections is not as clear as it seemed initially, and so far, a truly unifying concept is still lacking.”
The argument in favor of the hygiene hypothesis stresses that there has been a worldwide increase in allergic diseases, mainly in the developed world. There has also been a decrease in parasitic and bacterial infections, attributable to an increase in the use of antibiotics and immunization.
But Sorensen noted that allergy increases have been found in some societies and not in others, which points to a genetic influence.
“Asthma incidence is highest in the United States in the inner cities, where pollution and infections are the highest, so the hygiene hypothesis has certainly not protected our less fortunate kids,” Sorensen said.
He added that in some areas parasites, antiparasite immunoglobulin (Ig)E and asthma coexist. “If total IgE is very low, it is not allergy,” Sorensen said.
Furthermore, allergies rates do not improve among children who are taking antiobiotics. If a child improves on antibiotics, it is likely because there is an immune deficiency, Sorensen advised. “If you keep giving antibiotics, you are constantly altering the gut microbiota and probably promoting allergies.”
He suggests that clinicians avoid excessive antibiotic use unless it is clearly necessary and encourages clinicians not to stop immunization due to allergy fears.
Encouraging the right infant feeding, such as breast milk rather than cow-milk formula for neonates, may potentially curb the increase in allergies, according to Sorensen. “Once the patient is allergic, you have to avoid exposure,” he added.