BACKGROUND: There are limited data regarding the association of actinic keratosis (AK) and other types of nonmelanoma skin cancer (NMSC); studies investigating possible correlation of AK with melanocytic naevi are even scarcer. To our knowledge, there are no data examining the risk of AK in people using specific medications.OBJECTIVE: To investigate constitutional and exposure risk factors leading to AK and the coexistence of AK with NMSC and melanoma.METHODS: A multicentre hospital-based case-control study was performed in Finland, Germany, Greece, Italy, Malta, Poland, Scotland and Spain, including 343 patients with actinic keratosis (AK), 409 with squamous cell carcinoma (SCC), 602 with basal cell carcinoma (BCC), 360 with invasive melanoma and 119 with in situ melanoma, and 686 control subjects. Exposures were assessed by questionnaires that were partly self-administered and partly filled out by dermatologists. Unconditional logistic regression modelling was used to assess associations including the influence of phenotypic characteristics, presence of naevi, sun-exposure habits and certain drugs on AK risk.RESULTS: Differences in hair and eye coloration variably influenced the risk for AK, with red hair signifying a seven times higher risk [odds ratio (OR) 6·9, 95% confidence interval (CI) 4·34-11·00), and brown - compared with blue - eyes, about a 40% reduced risk (OR 0·61, 95% CI 0·13-0·92). The darker the skin phototype, the lower the risk for AK, with phototype IV exhibiting nine times less risk of developing AK. Some and many freckles on the arms were associated with an OR of 1·8 (95% CI 1·08-2·81) and 3·0 (95% CI 1·10-3·54), respectively, while overall number of naevi and high educational level were inversely associated with AK. Sun exposure, thiazide diuretics and cardiac drugs had a higher risk for AK. SCC was the most frequent (58%) skin neoplasm coexisting with AKs, followed by BCC (30%), melanoma in situ (12%) and invasive melanoma (6%).CONCLUSION: In this large case-control study from across Europe the expected associations were confirmed for known risk factors. Some possible new risk factors, including cardiac and diuretic drugs, were identified, creating a new field for further investigation in future studies.