Why are allergies increasing?

The incidence of atopic allergy is increasing in certain 'Western' countrie s but this remains unexplained. Various hypotheses with differing amounts o f evidence and/or relevance have been assessed, including increased awarene ss of the diseases, improved diagnostics, genetic susceptibility, psycho-so cial influences, allergen exposure, decreased immune-system stimulation, un derlying disease, anti-allergic therapy and pollution.