Seasonal variation in immediate skin test reactions.

Seasonal variation in the size of immediate prick skin tests was examined in relation to changes in seasonal pollen exposure. Immediate skin test reactions to serial 5-fold dilutions of: (1) a specific pollen during its season (short ragweed), (2) a specific pollen from an earlier season (tree), (3) a perennial allergen (D farinae, D pteronyssinus, or cat), and (4) histamine were examined at the projected trough of ragweed-specific IgE (2nd week in July), at the peak ragweed pollen count (3rd week August), at the estimated peak in ragweed-specific IgE (4th week in September) and at a time of no pollen exposure (2nd week in February). All 30 subjects had symptoms of rhinitis during the ragweed season and a 3 mm or greater wheal to: 100,000 AU/mL of short ragweed, 1:20 wt/vol of a tree exact, and a perennial allergen either 100,000 AU/mL of cat or 10,000 AU/mL of D farinae or D pteronyssinus. The median equivalent dose (dose of skin test material required to produce the median skin test index score) for the four time periods revealed significant seasonal differences. The reactions in October and February were significantly greater than those in July and August for all skin test agents. Histamine, ragweed, and trees showed maximal sensitivity in October, while perennial allergens demonstrated a peak in skin test sensitivity during mid-February.