Aeroallergen sensitization and upper respiratory allergies among patients living in rural and urban areas: Real-life exploration of the hygiene hypothesis

The number of people experiencing allergies has been increasing in the last decades. However, the increase in the global incidence of allergies observed is too fast and steady to be due to a genetic mutation. It may be due to environmental changes acting on some individual susceptibilities. According to what experts call “the hygiene theory”, the “excessive cleanliness” has been implied in reduced “microbial stimulation needed to enable normal development of the immune system”.1 Specialists in allergy and immunology explored this concept; it evolved into the broader notion that declining microbial exposure is a major causative factor in the increasing incidence of atopy in recent years.