Summarize this article:

Natural acne treatments can cause bacteria to enter into your pores, which can lead to an infection. If you don't treat an infection quickly, it can cause scarring, facial marks, and can be dangerous if it spreads. Get to a doctor if you have a pimple that becomes infected for antibiotic treatment. Look for pus oozing out of a pimple or red streaks in the skin surrounding pimples. These are surefire signs of an infection. Pain or sensitivity in the skin around a pimple could be a sign of infection as well.

Summary:
See a doctor if a pimple becomes infected.