Actinic keratosis (AK) is the main risk factor for the development of cutaneous invasive
squamous cell carcinoma (SCC). It represents the first sign of severe chronic ultraviolet radiation exposure, which has a clear significant effect. Nevertheless, the skin is exposed to many other exposome factors which should be thoroughly considered. Our aim was to assess the impact of exposome factors other than ultraviolet radiation (UVR) on the etiopathology of AK and
Bowen's disease (BD) and progression of AK to SCC and to design tailored prevention strategies. We performed an exhaustive literature search in September 2021 through PubMed on the impact of exposome factors other than UVR on AK, BD and SCC. We conducted several parallel searches combining terms of the following topics: AK, BD, SCC and microbiome,
hormones, nutrition, alcohol, tobacco,
viral infections, chemical contaminants and air pollution. Notably, skin microbiome studies have shown how
Staphylococcus aureus infections are associated with AK and AK-to-SCC progression by the production of chronic
inflammation. Nutritional studies have demonstrated how a
caloric restriction in fat intake, oral
nicotinamide and moderate consumption of wine significantly reduce the number of premalignant
keratoses and SCC. Regarding lifestyle factors, both alcohol and smoking are associated with the development of SCC in a dose-dependent manner. Relevant environmental factors are
viral infections and chemical contaminants.
Human papillomavirus infections induce deregulation of cellular proliferation and are associated with AK, BD and SCC. In addition to outdoor jobs, occupations such as industrial processing and farming also increase the risk of developing
keratoses and SCC. The exposome of AK will undoubtedly help the understanding of its etiopathology and possible progression to SCC and will serve as a basis to design tailored prevention strategies.