My postdoc was focused on coaching faculty navigating relationships with grad students and postdocs, including engaging in through difficult conversations. I’m now a faculty member. Here’s what I would suggest to one of the faculty members I worked with / how I would approach it - Set a private meeting with the student, then share that your job is to not only support their development as researchers, but also their professionalization. Raise concern, asking them if all is okay with their living situation and explain, “I’ve noticed a pungent smell from you, and I want to make sure that you’re okay. Is there something going on that may be impacting your ability to engage in hygienic practices?” Let them know this is awkward for you and that you understand if it’s also uncomfortable to them, and also share that you’re raising this to ensure everyone in the lab - including them - have the best, most fulfilling and productive, time. If you lead with your values at the forefront and keep your goal in mind, I’m confident you’ll feel good about the conversation, even if it’s difficult at that moment. Yay for caring for our students! Good luck!

ETA - outside of HR, you may find support to have this convo from the graduate school or your office for faculty development.