Time trends in the incidence of allergic contact dermatitis in older persons: a 24-year nationwide registry-based study

Age-related changes to the skin and prolonged exposure to chemicals can make older people prone to develop allergic contact dermatitis (ACD). However, few longitudinal studies have described trends of changes over time in the incidence of ACD in older people. Our objectives to study patterns over time in the incidence, demographics and etiology of ACD in an older population (aged > 65 years) in Finland. This retrospective, longitudinal nationwide study analyzed patient data gathered from Finland’s national healthcare registry for the years 1998 to 2022 by using the International Classification of Diseases code L23 set in the Dermatology clinics. The study population included 4,529 people, predominantly female. The incidence of ACD was 26.3 per 100,000 person-years and remained quite stable during the 24 years’ follow-up. However, there was a particular increase in the incidence of ACD due to ‘cosmetics’ and ‘other chemical products’ (rubber, cement and plastic). The most common L23 categories were ‘drugs in contact with skin’(24.7%), ‘cosmetics’ (23.9%) and ‘metals’ (18.5%). Over 20% of the patients had diagnostic codes for multiple ACD L23 categories. We demonstrated a high incidence of ACD in older people. There was a particular increase in ACD cases ascribed to ‘cosmetics’ and ‘other chemical products’. Eczemas are common skin diseases in older people and ACD should be kept in mind as a differential diagnosis for eczemas.