We often hear that allergies are becoming much more common and that in some way or other this is linked to the fact that the environment is continually deteriorating. But how much do we know about allergies and asthma and their connections to our surroundings? On the whole it can be said that, despite considerable research efforts, we are unsure on several essential points as to what causes allergy and asthma and even whether they actually are becoming more common.

To be allergic means that one is hypersensitive to specific substances (allergens); that one gets a powerful immune reaction even at concentrations which do not bother other people. There are many kinds of allergies: hay fever, asthma, food allergies, nettle rash, anaphylactic shock and eczema. It is estimated that in Europe around 10-30 percent of people have some form of allergy, by far most common being hay fever and nickel allergy. In the US, about 35 percent describe themselves as being allergic, whereas official estimates run at about 18.5 percent. Allergy is the sixth leading cause of chronic disease in the US.

Globally, asthma is one of the most serious allergies. Just under 6 percent or 15 million Americans have it, whereas more than 30 percent or 18 million Britons have asthmatic symptoms. Asthma causes the air passages to narrow. Unlike chronic bronchitis, for example, this narrowing is generally temporary and stops either spontaneously or after treatment.