Most of these kinds of apparent conflicts with the pill actually don’t have any real basis.
By all means, topical *anything* (that isn’t a transdermal medication, like a hormone therapy), is going to be fine. And there also aren’t verified issues with most herbal medicines and such.
For what can be issues, check out the info on this page:
http://www.scarleteen.com/birth_control ... ation_pill
And just FYI, since the pill doesn’t offer any STI protection, it’s generally smart to use condoms and other barriers with it anyway. An extra bonus of that is that it also offers backup birth control in case there ever is any effectiveness issue with your pill.