The Effect of Vitamin C on Histamine and Dust Mite Epicutaneous Test Responses: A Randomized Control Trial

Objective: Vitamin C has antihistamine properties, but its e!ect on allergic skin responses is unclear. This study aimed to evaluate the e!ect of vitamin C on skin wheal reactions to exogenous histamine and a known allergen during skin prick tests (SPTs). Methods: In this single-blinded randomized controlled trial, adults with allergic rhinitis and known positive SPT toward house dust mites were randomized into 2 groups: the intervention group received vitamin C (1000 mg daily for 7 days) and the control group kept a diet journal only. Repeat testing was conducted on day 8, and wheal sizes were measured using Image J software. Mean differences in wheal area (mm2) between groups were compared, and treatment effect sizes within groups were calculated using Cohen’s d formula. Results: Of 103 participants, 44 in the vitamin C group and 45 in the control group completed the study. Vitamin C led to a small, non-significant reduction in histamine-induced wheal size (-2.5 ± 11.57 mm2, Cohen’s d=0.30 vs. -0.92 ± 14.24 mm2, P=.56, Cohen’s d=0.08), but no reduction was seen for dust mite allergens (+4.48 ± 25.08 mm2, Cohen’s d=-0.20 vs. -0.16 ± 26.17 mm2, Cohen’s d=0.01, P=.40). Conclusion: Short-term vitamin C supplementation had a minor, non-significant suppressing effect on exogenous histamine but did not attenuate the skin allergen responses. Vitamin C may be useful for histamine intolerance, but this requires larger studies.