Hello WoolPulle
I regularly clean the mugs in the dishwasher. I can imagine that "wash by hand" is specified for safety reasons, so that the paint is not damaged/scratched.

Hello
I have had my cup for 4 years now. And I use it every day. I wash it in the dishwasher every day. After about 2 years, the colour has crumbled off. The mug now has a stainless steel look, which doesn't bother me. But the lid is not affected either. The mug is still leak-proof and does its job wonderfully.
Best regards