While there areveral "safe" sunscreen lotions on the market for dogs or even horses, there is NO SAFE CHEMICAL/LOTION SUNSCREEN FOR CATS.
As of this time, only sunblock clothing is the the 100% safe option.
90% of what you put on a Sphynx Cat's skin goes into their bloodstream. They have extremely thin skin and many less layers of dermis than humans. Zinc ( no matter how it's packaged) is toxic to them, as are most chemicals found in any effective sunscreen.
Currently the only way to prevent sunburn, and/or skin cancer is to keep your pet out of the sun. But cats (and dogs) and sun are like peanut butter and jelly. Or whatever two things that go great together.
Sun comes through the windows, and the cats melt. No, we can't cover the ears, or the tails, or every inch. But we cover what we can.
The fabric we use for our sphynx cat sunblock shirt blocks at least 97% of the sun's UVA and UVB rays. UPF (Ultraviolet Protection Factor) represents the ratio of sunburn-causing UV without and with the protection of the fabric, similar to SPF (Sun Protection Factor) ratings for sunscreen. While standard summer fabrics have UPF ~6, sun protective clothing typically has UPF ~30, which means that only 1 out of ~30 units of UV will pass through (~3%). See more at Wikipedia Sun Protective Clothing page, http://en.wikipedia.org/wiki/Sun_protective_clothing
According to the Skin Cancer Foundation,
"Clothing is the single most effective form of sun protection. It is our first line of defense against the sun’s harmful ultraviolet rays."
Nearly 3.7 million skin cancers are diagnosed in the US annually, and the vast majority of them are caused by solar UV radiation (UVR). UVR also causes up to 90 percent of the visible changes commonly attributed to aging, such as wrinkles, brown spots, and sagging skin. Fortunately, clothing can absorb or block much of this radiation.