What is the ruling on biting the dead white skin around fingernails and on toes?

We advise the questioner to ignore obsessive thoughts and to strive to abandon nail-biting. As for the ruling on washing the exposed skin after biting nails or feet during ablution (wudu') or ritual bath (ghusl), it is obligatory to wash it because it has become part of the outer body, as mentioned by An-Nawawi in "Al-Majmu'".