These are much like absorbent bath towels, but many have a key difference: a no-slip backing typically made of latex. Bathroom rugs should be washed separately according to label directions. Washing rugs with anything else in the machine — particularly towels — will load them with hard-to remove lint. Latex-backed rugs may be either air-dried or tumble dried on a very low setting.
Some bath rugs were made with rubber backing, which cannot by placed in a dryer. Allow these to air dry instead.
Rugs with a deep color when new should be washed separately before being used to prevent dye transfer to your feet.
Reference:
Jeff Bredenberg, editor, in Clean It Fast, Clean It Right: The Ultimate Guide to Making Everything You Own Sparkle & Shine.