Background: Aquagenic keratoderma is a rare transient disease that occurs after water immersion and disappears shortly after drying. Most cases involve the palms and fingers bilaterally but it can also affect the soles. Few cases have been associated with drugs but its pathogenesis remains unclear.Main observation: We report a 60-year-old man with a 30-year-history of aquagenic keratoderma of the right palm without associated hyperhidrosis or history of drug intake. After unsuccessful treatment with 15% aluminium chloride hexahydrate gel, botulinum toxin A injections led to significant improvement within 2 weeks.Conclusions: To our knowledge, this case is the first report of idiopathic unilateral aquagenic keratoderma in the medical literature. It is the third report of successful treatment with botulinum toxin A which is in favor of a role of sweat glands in the pathogenesis of aquagenic keratoderma.

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ImportanceThe common use of isothiazolinones as preservatives is a global cause of allergic contact dermatitis. Differences in allowable concentrations of methylisothiazolinone (MI) exist in Europe, Canada, and the US.ObjectiveTo compare the prevalence of positive patch test reactions to the methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) combination and MI alone in North America and Europe from 2009 to 2018.Design, Setting, and ParticipantsThis retrospective analysis of North American Contact Dermatitis Group, European Surveillance System on Contact Allergies (ESSCA), and the Information Network of Departments of Dermatology (IVDK) databases included data from patients presenting for patch testing at referral patch test clinics in North America and Europe.ExposuresPatch tests to MCI/MI and MI.Main Outcomes and MeasuresPrevalence of allergic contact dermatitis to MCI/MI and MI.ResultsFrom 2009 to 2018, participating sites in North America and Europe patch tested a total of 226 161 individuals to MCI/MI and 118 779 to MI. In Europe, positivity to MCI/MI peaked during 2013 and 2014 at 7.6% (ESSCA) and 5.4% (IVDK) before decreasing to 4.4% (ESSCA) and 3.2% (IVDK) during 2017 and 2018. Positive reactions to MI were 5.5% (ESSCA) and 3.4% (IVDK) during 2017 and 2018. In North America, the frequency of positivity to MCI/MI increased steadily through the study period, reaching 10.8% for MCI/MI during 2017 and 2018. Positive reactions to MI were 15.0% during 2017 and 2018.Conclusions and RelevanceThe study results suggest that in contrast to the continued increase in North America, isothiazolinone allergy is decreasing in Europe. This trend may coincide with earlier and more stringent government regulation of MI in Europe.