This is a problematic area. You can use suncream on cats but you have to be careful about how it is used. In general, domestic cats like to lie in the sun. Cats with white non-pigmented areas of skin can suffer serious skin inflammation which the doctors call solar dermatitis. It occurs mainly on the nose and ears. An unprotected cat might develop squamous cell carcinoma (1 in 300 can suffer skin cancer). This is a malignant tumour which spreads locally destroying surrounding tissue.
White Cats: 1 in 300 chance of skin cancer through sunlight
Some cats will tolerate sunblock cream on those vulnerable areas and if so it should be SPF 30 or more. Most cats will simply wash it off and then ingest (swallow) the sunblock cream.
Therefore, there are special sun creams for cats and dogs which don’t contain zinc oxide. According to ASPCA sun creams containing zinc oxide (typically found in sunblock creams) and a group of chemicals called salicylates are toxic to cats. It might be a gradual process but repeated exposure to zinc oxide can causing toxicity which, they say, can damage the red blood cells. Salicylates might irritate the skin and cause it to become inflamed.
You need to pick a veterinarian-approved sunscreen and therefore I would suggest you contact your vet to discuss this.
I would argue that is the sensible way to proceed because I’m not sure that you can completely trust online suppliers of pet sunscreen which is a shame because of the convenience. I will refer to one example. In the UK, Pets at Home, a well-known retailer of pet products, sell Filtabac Antibacterial Sunblock Cream (Web Exclusive). The information provided online states that the ingredients are titanium dioxide and zinc oxide cetrimide. Cetrimide is an anti-septic added to the sunscreen.
As you can see, their product contains zinc oxide which the ASPCA (a trusted American organisation) say is toxic to cats. What is going on? Is Pets at Home being careless? The Pets at Home products is recommended by those who have used it although the comments refer to its use on horses and dogs.
Filtabac Antibacterial Sunblock Cream also contains an antibiotic which helps wounds to heal. However, one person commented; Kathy Hill, says that “there is only a very small amount of zinc oxide and this is inert so it cannot be absorbed by the gut”. I cannot confirm whether that is true or not and therefore common sense dictates that you should discuss it with your veterinarian.
There is certainly some use in using sunscreen for outdoor cats. You just need to be aware of the potential downsides.