what would happen if you apply self-tanner on area around eyes? the label on all of them says not to do that, why is it this way?

i use self-tanner which gives just a hint of tan. but i've seen people who apparently uses strong self-tanner and it makes their eyelids look strange, because the eyelids are white while face and body is brown.
FYI some self-tanners are dedicated both for body and face. anyway, face tanners can't be applied on 'eye area skin' as well. anybody knows why?