I’ve worked as a doctor since 1980, at one time when working with heroin users in methadone clinics I noticed that genuine heroin users had a very distinctive body odour, which I found helpful in assessing them. This was only evident when there was no air conditioning. The odour would linger in the room once the patient left.
There is a tradition in medicine of smells related to particular illnesses, which no one talks about any more. It’s been replaced with externalised tests, but you can tell a lot from how people smell.
sweaty, slightly acrid, slight chemically smell, unnatural.