What are the causes of allergy?
While no one's decoded the exact reason for the rise in allergies, the big picture offers several clues.
In the 1980s David Strachan, now a professor of epidemiology at the University of London, put forward the 'hygiene hypothesis’. This is the idea that poor hygiene and exposure to infections in early childhood has a protective effect against allergy. Children raised on farms in close proximity to animals tend to show fewer allergic reactions in later life. But the 'hygiene hypothesis' is far from proved - there are signs that infection may kick off an allergy in some cases. Population studies have also been suggestive too: children from East Germany had a far lower incidence of allergic diseases until the fall of the Berlin Wall. With access to a consumerist lifestyle, allergies dramatically increased.
Poor diet during pregnancy and infancy may cause allergies - especially if there is a lack of Vitamin E, and possibly Vitamin D and zinc. Breastfeeding may protect against allergy in the short term, but it's not known whether this gives lifelong benefit. Is easy access to junk food and food additives making the rising generation susceptible to allergy?
Sometimes allergies are caused by a large number of allergens in the air - asthma epidemics in Barcelona have been linked to 'soya bean dust storms' as cargoes of soya are unloaded at the docks.
Others point to the large number of chemicals in the modern home. A report by Greenpeace lists the thousands of chemicals found in common household appliances and carpets. With so many factors in play, and with their combined effect unknown, it is hard to pin down the most problematic. The link between external pollution in allergy is still debated – a report Does Air Pollution Cause Asthma? is due out from the Department of Health’s Committee on the Medical Effect of Air Pollutants in 2008.
While it’s true that factors like a high pollen count and living in damp conditions exacerbate allergies, it doesn’t follow that this is straightforward cause and effect. Talking to the House of Lords Committee about allergy, Professor Warner, a consultant paediatrician expert in allergic disorders, commented ‘everybody lived in damp, cold housing one hundred years ago and there was much less allergy,’