Variation in skin reactivity inhalant allergens estimated by the end-point technique.

Skin prick testing is commonly used to diagnose IgE-mediated sensitization to allergens, whereas the longitudinal variability in positive/negative results can be used for clinical and epidemiological purposes. Few publications have investigated the longitudinal variability in skin reactivity, and most studies have concluded that seasonal changes in exposure to environmental allergens are paralleled by a change in skin reactivity. Our trial investigated the relationship between variations in skin reactivity and seasonal exposure to allergens in sensitized subjects, by use of a sensitive method-the end-point technique. Forty-three patients monosensitized to inhalant allergens were selected, and the skin prick end-point technique with serial 1:4 dilutions of standardized commercial allergens was used to assess skin reactivity. Twenty-two patients sensitized to pollens with a short pollination period were tested before and after the pollen season, whereas the other 21 patients sensitized to house dust mites or to a species with a long pollination period such as Parietaria were tested in the same month 12 months later. Patients tested with the end-point technique showed a large interindividual variability in skin reactivity. None of the patients in either group showed a decrease in skin sensitivity with time whereas 9 out of 43 showed no change and 34 out of 43 showed an increase (p < .0001). According to our data, skin reactivity increases in sensitized subjects over time, and this increase seems not to have a circannual rhythm related to the seasonal exposure to environmental allergens, since it can be detected both in pollen- and mite-sensitized patients after a 12-month interval.