Illusory Disguise changes how you look, and if you heighten it to second level it changes how you smell and sound. But does it change how you feel? If a human uses Illusory Disguise to disguise themselves as a lizardman, and someone touches them, will they feel like they have skin or scales?
So if someone touches suchs a disguised person they would get a perception check to notice the difference. IF they fail they don't notice anything odd.