Actinic keratosis in a finger. Solar keratosis (actinic keratosis) is an erythematous scaly symptomless patch. It does not react to regular moisturizing creams or topical corticosteroids as the similar-looking eczemas do. Differentiation from carcinoma in situ of the skin (Bowen's disease) is sometimes difficult, because both actually belong to the continuum solar keratosis – carcinoma in situ – squamous cell carcinoma. Carcinoma in situ is often thicker and more keratinized, and the surface is more easily bleeding.

Picture: Raimo Suhonen