Kind of true, but it's more like an ant scent marking. They know this is a place that's safe (rats have been here). With good absorbent natural substrate in the cage, and wiping down their free roam area if needed, it's mostly unnoticeable. I like to compare it to a person needing to change their t-shirt every day, probably not a deal-breaker for interacting, unless you don't clean for way too long.