Background: Paederus dermatitis (PD) is a skin reaction to a chemical substance called paederin that emanates from Paederus spp.
Objective: To investigate the clinical manifestations and progression, seasonal variation, and environmental factors associated with PD among patients attending the outpatient dermatology clinic of Siriraj Hospital.
Materials and Methods: This prospective cohort study included patients who were diagnosed with PD at the Department of Dermatology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand during the October 2017 to July 2018 study period. Socio-demographic and environmental data were collected via questionnaire.
Results: Twenty-five PD patients (16 females, 9 males) were included with a mean age of 40.9 years (range: 17-69). The most common sites were the upper and lower extremities. Erythema, linear, and kissing lesion was found in 100%, 32%, and 28% of patients, respectively. Seventy-six percent of patients demonstrated more than one lesion. Eighty percent of patients lived in Bangkok, and 44% of patients had a home near a farm or forest. Fluorescent lighting was used in the homes of 24 patients. All 25 cases were treated with topical steroid, and some cases received other supportive regimens. Two patients had post-inflammatory hyperpigmentation as a complication; however, only 7 of 25 patients attended the scheduled follow-up visit.
Conclusion: PD presents throughout the year, but the most active month is December. Skin lesions vary from mild irritant dermatitis to severe dermatitis, and the average time to complete cure is 12 days. History and clinical manifestation are essential for accurate diagnosis.