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What鈥檚 behind the rise in allergies?

Cleanliness is next to godliness, as they say, so for those who are a little less fastidious, the idea that dirt could protect from allergies might have a certain appeal.

First proposed in 1989 by epidemiologist David Strachan, the thinking behind this 鈥溾�� was that modern life has become more hygienic, leading children to catch fewer infections. This somehow predisposes them to develop allergies, perhaps because their immune systems have been incorrectly trained. If so, allergies are the price people in developed nations pay for massively reduced infant mortality.

It is an idea that caught hold with the public, but it doesn鈥檛 fully add up. We now know that childhood infections don鈥檛 seem to make you any less likely to develop allergies. And major cities like London and New York had 鈥� long before the idea was put forward. Water chlorination and separate sewage systems made cholera and typhoid infections rare. And if clean living is to blame for allergies, it doesn鈥檛 make sense that it took 40 years for asthma to begin to rise. Since 1960, developed countries have seen only minor changes in hygiene, so what prompted the sudden and recent surge in food听allergies?

What we do know is that older siblings are more likely to get some allergies than younger siblings, and that children who grow up in big families or on farms are less likely to develop them. Rather than cleanliness in the home or catching infections, the key factors seem to be spending time with other children and being outdoors in early life听鈥� probably because this maximises the range of microbes we meet as infants. As people in the West moved towards spending more of life indoors and in urbanised environments, as is now happening in nations like China, they may have lost contact with particular microbes that have helped hone the human immune system for millennia. This is known as the 鈥溾�� hypothesis.

How such friendly microbes may help prevent our IgE system from misfiring is still largely unclear. But we are beginning to understand that the different bugs living in our bodies can affect many aspects of our health. It is possible that some of them help quieten down elements of the immune system, preventing any overreaction. You are unlikely to restore these missing microbes simply by neglecting your personal hygiene, however. And by the time you are an adult, there may be little you can do to shift your microbiome听鈥� it is probably too late to up sticks and move to a farm.

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Can exposure cure my allergy?

If you have ever heard someone claim they have cured their hay fever by spending time outdoors or that a daily serving of honey听鈥� which contains pollen grains听鈥� has built up their immunity, don鈥檛 fall for it. 鈥淭here鈥檚 not much evidence for that,鈥� says听Syed Hasan Arshad at the University of Southampton, UK.

Similarly, forcing yourself to eat peanuts if you are allergic to them is a bad idea, as is living with a pet in the hope that one day you will get along fine.

The idea is grounded in sensible science, though. Clinical injections of small, increasing doses of an allergen can desensitise the immune system to some allergies. When it is administered over several years, there is good evidence that this treatment can work for allergies such as bee and wasp stings, as well as nasal inflammation caused by grass pollen, tree pollen or house dust mites, says Graham Roberts of the University of Southampton, UK.

The treatment, often known as allergen immunotherapy or 鈥渁llergy shots鈥�, seems to gradually build up the amount of exposure the immune system can handle. But as the technique can prompt swelling or itching near听the injection site, and in some cases anaphylaxis, breathing problems and collapse,听it should be administered by a听clinician at a hospital.

Some experimental peanut immunotherapies have had good results in听children, providing lasting effects, but patients need to keep eating peanuts to maintain the protection, says Roberts. Immunotherapy seems to work well for cat听allergies too, but is less effective for dog听allergies.

However, this isn鈥檛 something you can mimic yourself by frolicking in the grass or buying a cat 鈥� in fact, doing so is likely to make the problem worse.

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Can I prevent my child from developing allergies?

It was gospel medical advice for years. Women听were urged to avoid commonly allergenic foods such as peanuts during pregnancy and breastfeeding, and were told that their children shouldn鈥檛 eat these foods during their first few years of life. The advice was designed to prevent kids from getting allergies. But in the past few years, we have discovered that, in most cases, this was wrong.

Whether women eat allergenic foods during pregnancy turns out to make no difference, and they are no longer advised to avoid them.

But certain things do seem to have an effect. A study of nearly 6000 infants last year found that being exclusively breastfed during the first four months of life seems to be linked to a听reduced chance of developing hay fever in听low-risk children.

But breastfeeding isn鈥檛 the whole story. Evidence is growing that, instead of avoiding allergenic foods, it may be important for high鈥憆isk children听鈥� those with moderate or severe eczema, or those whose parents or siblings have allergies听鈥� to encounter them early on. Those that are introduced to peanuts between the ages of 4 months and 11 months are 81 per cent less likely to develop a peanut allergy by the time they are 5. Similarly, children who begin eating eggs at the age of听4听to 6 months are less likely to develop egg听allergies.

Some guidelines in the US and Australia now ingredients from the age of 4 to 6 months, although the World Health Organization still recommends giving babies nothing but breast milk until they are 6 months old.

The key appears to be exposing a baby鈥檚 immune system to potential allergens before they have a chance to develop allergies听鈥� a narrow window of opportunity.

But how this works is still unclear and in many cases the evidence is contradictory. Eating peanuts early in life may be beneficial, but growing up in a home where a lot of peanuts are eaten .

The idea that a lack of 鈥済ood鈥� microbes in the gut may be to blame for rising allergies has听prompted interest in using prebiotics to听change the gut flora of a mother or her infant in order to protect against allergies. However, there is .
This article appeared in print under the headline 鈥楢llergy explosion鈥�