For practical implementation, it would probably be simplest that the player’s hygiene would have a simple effect of allowing entities to detect you via smell for longer than normal. Longer trails when moving, more smell persists when left behind in any given spot.
Perhaps as a mildly hilarious addition, if your hygiene was poor enough or you’d been exposed to a very noticeable odour, other players could even pick up on this with their own sense of smell.