A reader wrote to me with a truly disgusting tale of the unhealthy and unacceptably low level of personal hygiene of a very smart and motivated graduate student. This raises the interesting but difficult question of how much an adviser can do in these situations. Can we demand a certain level of personal hygiene of our graduate students? Can and should these demands be enforced?
I hasten to note that this reader is dealing with an extreme situation. This is not the case of preferring that someone not sweat, or something of a similar level.
If the unsanitary behavior is so revolting that others in the group (including the adviser) find it nauseating to work with a particular student, it could be that the student has a serious physical or emotional problem that needs attention by the university health center. I have never been in the situation of having to ask a student to seek help for this type of problem, so I don't speak from experience here, but I think I would first inform someone in my department of the situation (e.g., the department chair, the grad adviser), perhaps consult with the campus health center, and then talk to the student about the problem and the need for him/her to get help.
You can't force a student to get medical help, but you can do things to minimize the impact of the situation on those who must work with the student. Note that I focus on students here because that is what the e-mail was about, but of course there are faculty with unfortunate personal hygiene issues as well.
It is also reasonable, in extreme cases, to set limits on what the student can and cannot do in terms of access to facilities and interactions with others. These limits should be very clearly stated and discussed with the student, however difficult it is to have that conversation. Someone who is just a slob (as opposed to mentally ill) may then be motivated to clean up, once it is clear that continued revolting personal habits have negative consequences for themselves.
It may be a good idea to have another faculty member or an administrator or even a counselor in the room when you, the adviser, has a conversation with the student about these topics. You don't want to humiliate or appear to gang up on a student who may be having severe problems, but you also want to make sure that conversations that touch on issues of a rather personal nature are dealt with in a professional way by those better equipped to deal with them.
If the student cannot or will not be helped, but does excellent work despite causing widespread revulsion in all who come into contact with him/her, perhaps there is a way for that student to work in near-isolation. That doesn't sound like a such a healthy or even good solution for the student, but the other options seem even worse. It is difficult to imagine what kind of career such a student could have upon obtaining a degree.
Perhaps others who have encountered similar situations as advisers will have better advice than I have been able to muster.
6 months ago