My housemate's bedroom literally smells like a homeless person?

You know that really distinct smell, I don't even know what it is - but only homeless people smell like that. Well I had never actually been in or seen his room until a few days ago. That night, he left his door open by mistake before he went out somewhere. I had to go in there to get the cats out and close the door so they couldn't get in (his window was open and they are indoor cats). I literally felt sick just standing in there from the smell.

He has bipolar and I'm sure he's going through a depression cycle at the moment as he has hardly left his room the past couple of weeks.

what the hell is causing that smell I didn't think anything other than a homeless person could smell like that?
My housemate's bedroom literally smells like a homeless person?
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