The only way to know for sure is to view them under blacklight in a dark room. Last year I bought a t-shirt in a favorite pattern from Bass Pro, I hung it in the closet where I keep the rest of my hunting clothing. Later, as I was testing UV killer on a different garment I saw that the brand new shirt glowed like a night light when the UV struck it. Does it spook deer? Most definitely, it's happened to me several times, but not since I began to pay attention to my UV signature as well as scent and movement.