There is little doubt that the number of reported allergies is increasing in the U.S. and the UK. Research published in 2007 showed the number of hospital admissions in the UK for food allergies had increased by 500% since 1990. Number of Americans with allergies is two to five times higher now than 30 years ago.
Here are some of the reasons why the allergies are becoming more common:
- Hygiene theory. Living cleaner lifestyles means the immune system has fewer germs to deal with and may overreact when it comes into contact with harmless substances. Exposure to microbes explains some of the inverse relation between asthma and growing up on a farm, according to a 2011 NEJM study. However, promoting the hygiene theory for allergy prevention as "eat dirt hypothesis" does little to convince the parents.
- Allergen exposure (exposure to substances which provoke an allergic immune reaction). It is clear that a high exposure to dust mite increases the risk of dust mite allergy. Spring allergies now start sooner and fall allergies end later, thanks to global warming.
- Atmospheric pollution. Chemicals in the air are provoking an immune response, for example, diesel particles serve as a vehicle that carries pollen deeper in the lungs.
- Lack of sunlight exposure and low vitamin D level. There is a North-South gradient in the Northern hemisphere - allergic disease and anaphylaxis are more common in the North and their prevalence decreases as we move south.
- Mother's diet. Pregnancy and breastfeeding could offer protection against allergies. However, the studies regarding avoidance of food allergens are contradicting, for example, early introduction of puffed corn covered with peanut butter may protect Israeli infants from development of peanut allergy. There are no evidence-based recommendations for a specific diet for prevention of asthma and allergies in early childhood (http://goo.gl/j3Al8).
- Excessive use of dichlorophenol pesticides may contribute to the increasing incidence of food allergies (Annals, 2012, http://buff.ly/UYEbLz)
The rise and rise of allergies. BBC.
Why your allergies are bugging you. CNN, 2011.
Nothing to sneeze at - There are many hypotheses as to why allergy rates are soaring worldwide. CMAJ, 2011.
Shorter duration and nonexclusivity of breastfeeding are associated with increased risk of asthma symptoms in children. ERJ January 1, 2012 vol. 39 no. 1 81-89.
Image source: OpenClipArt.org, public domain.