This Morning, I Woke Up With A Couple Rust-like Stains

This morning, I woke up with a couple rust-like stains on my right hand.(on my palm, fingers,thumb) this isn't the first time this has happened. It's happened two more times...that I've noticed. It will not wash off! I haven't used any self-tanning lotion...or anything that would stain your hands. I'm not sure what it is...it doesn't itch or irritate me, I just don't understand why I keep getting it.