November is Pet Cancer Awareness month.
White cats, especially with white faces and ears, are at risk to develop solar-induced carcinoma (skin cancer). It usually starts like a crusty sore on the ear tips or on the pink nose. To prevent squamous cell carcinoma we recommend these cats be indoor only and if they are sun worshippers apply pet or baby-friendly sunblock to their ears. Indirect light (such as light through window glass) certainly decreases risk. I would apply sunscreen if they are always at a window or under a skylight.