Can you use something for external use only internaly?

No, and here is an example. If you have some shampoo it is to be used "externally"on your hair and to take it internally (i.e. to swallow it would make you sick). So, as a rule if it says for external use only, it should not be put into your mouth,anus,eyes,ears,nose,vagina or any opening to your internal body.