Seasonal Variation in Contact Hypersensitivity to Parthenium in Patients of Parthenium Dermatitis

BACKGROUND: Titer of contact hypersensitivity (TCH) is a measure of contact hypersensitivity to an allergen in an individual. Clinical severity of Parthenium dermatitis varies with season. However, the effect of seasonal variation on the TCH as determined by patch test to Parthenium has not been studied. Objective: To study the effect of seasonal variation on TCH to Parthenium hysterophorus in patients with Parthenium dermatitis. MATERIALS AND METHODS: It was a prospective investigational study on clinically and patch test confirmed patients with airborne contact dermatitis to P. hysterophorus. The TCH values at baseline and after 6 months were recorded. The patients who were recruited in summers (April to September) and whose repeat patch test and TCH were determined in winters (October to March) were identified as Group I and those who were recruited in reverse order were identified as Group II. RESULTS: The study had 47 patients, of which 23 were in Group I and 24 in Group II. Mean TCH in Group, I (summer to winter) in period I (summer) was 0.11 ± 0.28 whereas that in period II (winter), was 0.76± 0.41. Similarly, mean TCH in Group II (winter to summer) in period I (winter) and period II (summer) were 0.34± 0.44 and 0.166± 0.32, respectively. The difference in TCH values (95% confidence interval) in the two groups with a change of season was −0.41 (−0.58, −0.24) (P < 0.0001). CONCLUSIONS: TCH values in Parthenium dermatitis are lower in the summer season, indicating increased sensitivity to Parthenium allergen in summer.