ABSTRACT
The last two decades have witnessed a consistent and worrying increase in the occurrence of allergic diseases of all types. A series of cohort studies in which similar survey methods have been used, reveal increases not only in the developed world but also in those countries where adoption of aspects of the western lifestyle is prominent. There have been numerous attempts to link these trends to particular aspects of the western lifestyle, but no single one satisfactorily explains the changes and differences in disease demography. In some countries, such as Papua, New Guinea and Australia, increased exposure to indoor allergens, such as house dust mite, has been strongly incriminated while, in others, it is stated that reduced exposure to gastrointestinal or respiratory infections in early childhood is responsible. Alterations in diet, overuse of antibiotics in infancy, exposure to air pollutants inside and outside the home, and differences in exposure to microbial products such as CpG oligonucleotides and lipopolysaccharide all have their advocates. While all of these environmental factors are capable of influencing the emergence of atopic disease, it seems most likely that a combination of factors interfacing with a susceptible genotype is where the answers are most likely to lie. Major advances will occur
2 Holgate
when a clearer understanding is obtained about the multiple susceptibility genes that underlie atopic sensitization and its expression in specific organs.
