When allergies go west

摘要

Germs can be good for us. This 'hygiene hypothesis' claims the urban 'Western' lifestyle, with its relatively limited exposure to infectious agents during childhood, might be behind the post-war epidemics of asthma, eczema and food allergies. But can the explosion in allergies in the developed world really be explained so simply? A more complicated theory is emerging. For, while it is apparent that there is something about Western living that increases the risk of developing allergies, research has shown that it's not just a culture of antibacterial soaps, antibiotics and excessive cleanliness that's to blame. There is evidence to suggest there is more about the way children are raised -where they are raised, what they are fed and how many siblings they have - that influences their burgeoning immune systems. It's not just that their exposure to microbes or potential allergens seems to be limited. Sanitary living conditions disrupt the delicate balance between our bodies and a complex ecology of microbes and parasites with which we co-evolved, and through which our immune systems are balanced and regulated (see 'Gut reaction', page S5).