Revealing mistake: During the scene where the military loses control of London, and their snipers are told "all targets are free", you can see heavy padding beneath Infected/civilian victims' shirts, etc, as they're shot. Presumably it's to stop them injuring themselves when they fall over, or to hold apparatus for the blood effects, but it's too bulky to be part of the characters' clothing.
Revealing mistake: Fire proof gloves appear on Doyle's hands when he is on fire.
Answer: I suspect that it's really not that simple. Remember that in the first film, Jim was lying alone in a hospital bed for some considerable time before waking to the deserted London. He would certainly not have smelt clean and fresh, yet he was still clearly detectable as prey by the infected. While being nice and clean makes it easy for them, it seems clear that it's not the sole indicator that triggers an attack.
Tailkinker ★