At the beginning of each spring allergies come back, bringing with them their share of sneezing, headache, blocked nose. They are contracted through the food, animal, plants and numerous chemicals. This is one of the most common and most deadly diseases that we know, however, there 100 years, these allergies do not exist. On a marginal condition affecting mainly the wealthy classes, allergy has become the archetype of the "disease of civilization" and now affects a quarter of Europeans. Why are we more likely to suffer from this disease?