Hair's tha thing....When purchasing products for chemical and coloring services most companies advise you to base your hairline, nape ears etc with petroleum in order to prevent staining. Some companies even provide you with small packets. One concern I see many bloggers and followers in the hair community discussing is the use of petroleum. It "suffocates the scalp", "it's too greasy", "hard to wash out".
If you didn't already know, here's a great tip. Instead of using petroleum, you can use your favorite condish or a cheapie to base those areas. (I use either or,they both work great). It's easy to rinse out and not only does it prevent staining just as effectively but your strands are getting added conditioning while you perform your chemical services!
Try it and let me know how you like it - Happy Hair Growing!