Age‐dependency of sensitization to aero‐allergens in asthmatics

Skin reactivity (intracutaneous test) to histamine and allergens was studied cross‐sectionally in a Dutch asthmatic patient population from childhood to old age (4–75 years). It was found that the histamine skin reactivity rose significantly (p<0.05) during childhood, was significantly higher in the 10–15‐year age group, and was constant between 20 and 75 years of age. The mean wheal index (histamine ratio) of all allergens was constant during childhood, and decreased after the age of 25 for grass pollen and house‐dust mite and after the age of 15 for the other allergens. The prevalence of a positive skin test decreased with age, except for grass pollen. During childhood the indoor allergens, cat dander and house‐dust mite, were the most important, while after the age of 15 sensitivity to an outdoor allergen, grass pollen, increased markedly. At all ages house‐dust mite was the most important allergen. After the age of 25 the prevalence of every allergen declines. The prevalence of a positive skin test to Cladosporium was unexpectedly high in childhood (10–40%). It can be concluded that the prevalence of a positive skin test declines with age, except for grass pollen. The degree of sensitization in asthmatics peaked in the age groups between 20 and 40 and sensitivity to indoor allergens developed earlier than sensitivity to outdoor allergens.Clinical aspectsSkin tests producing immediate wheal and flare reactions are widely used for the detection of allergy in patients referred for asthmatic prohlems. For good evaluation of a skin test it is important to know the influence of age on skin reactivity. In this study we evaluated the wheal index (histamine ratio) of the skin test and the prevalence of a positive skin test using a set of 6 standardized common aero‐allergens and one non‐standardized, cross‐sectionally, in a Dutch asthmatic patient population (4–75 years). Since standardized allergens were used, the prevalences hetween the different allergens could be compared. It was found that the histamine skin reactivity peaked at the age of 15 and was lower in all other age groups. Therefore, when comparing skin test results in different age groups, it may be important to use wheal indices instead of absolute values. Except for grass pollen the prevalence of a positive skin test decreased with age. During childhood indoor allergens are the most important, while after the age of 15 sensitivity towards outdoor allergens increases. Honse‐dust mite is the most important allergen at all ages. Surprisingly, a fungal allergen (Cladosporium herharuni) was found to he of significance in young children (prevalence 10–40%). The prevalence of at least one positive skin test in asthmatics declined with age, while the degree of sensitization (expressed as the mean wheal index) peaked in young adults (20–40 years of age).