The basic principle with regard to the man’s Awrah is that it is not permissible for his mother or sister to see it, because the Prophet (Sallallahu Alayhi wa Sallam) said: Guard your Awrah [do not let anyone see it] except from your wife or female slave. (Abu Dawood). But it is permissible for a sister to wash her brother if he is unable to clean himself and he does not have a wife who could serve him, and there are no men who could do that for him, because it is permissible to uncover the Awrah and touch it in cases of necessity and great need. While she is able to avoid looking at it or touching it, she must avoid doing that, and it is better to use a barrier such as a piece of cloth or gloves, and the like.