PDE5A and actinic keratosis: It is likely that the small observed increase in the risk of malignant melanoma among PDE5 inhibitor users is explained by higher sun exposure among PDE5 inhibitor users; this is strongly suggested by the increased risk of other diseases related to sun exposure among PDE5 inhibitor users and by the strong association between solar keratosis and subsequent PDE5 inhibitor use, which implies that men with high sun exposure were more likely to become PDE5 inhibitor users.