INTRODUCTION: Childhood irritant contact dermatitis (ICD) is the most common cause for developing chronic hand eczema as an adult. The COVID-19 reopening in Denmark included regulations introducing frequent hand washing. The aim of the present study was to evaluate if frequent hand washing increases the incidence of ICD in children. METHODS: We conducted an observational study in Denmark during the reopening of schools and daycare facilities for children aged 0-12 years (April 22nd to May 1st 2020). A questionnaire was sent out to parents in four municipalities consisting of 20 questions about frequency of hand washing, use of hand sanitiser, symptoms of ICD, atopic dermatitis, allergy and predispositions. RESULTS: The study included 6,273 children. In children without any prior symptoms of dermatitis, 42.4% experienced ICD (dry, red and itchy skin) due to increased hand hygiene. Schoolchildren had a 1.5 times greater relative risk of developing ICD than preschool children. Frequency of hand washing was a strong risk factor, whereas this was not the case for alcohol-based hand sanitiser. Hand washing 7-10 times/day and >10 times/day increased the relative risk by 1.83 and 2.23 times, respectively. CONCLUSIONS: A higher frequency of hand washing during the COVID-19 reopening increased the incidence of ICD in children. Hand hygiene is essential in our fight against novel coronavirus, but prophylactic initiatives are important to reduce the possible long-term consequences of ICD in children. FUNDING: none TRIAL REGISTRATION: Clinicaltrials.gov (NCT04375410).