Allergy has a very strong hereditary component but even in identical twins,
concordance for the development of allergic disease can be as low as 50%.
This suggests that there is a very strong environmental influence on manife
stations of sensitization. To what extent environment might have an influen
ce on the ontogeny of sensitization antenatally has hitherto not been a foc
us of much research. However, circumstantial evidence suggests that this ma
y be important.