Allergic sensitization, an important risk factor for allergic diseases such as asthma and rhinitis, has increased worldwide. Almost half of the young adult population is sensitized to common airborne allergens. Parallel, the prevalence of asthma and clinical allergy also increased all over the world. Allergic diseases are the most common diseases among children, adolescents and young adults in Sweden. Among adults, 8-10% have asthma, 30% rhinitis and 11% eczema. Among children and adolescents around 5-8% report food allergy. Part of the increase in asthma prevalence is related to changes in diagnostic criteria and increased awareness in the population. The increase may have levelled off in some areas.