If you've reached a certain age, chances are you've battled a pimple or two. For many people, a dab of basic blemish cream does the trick, but some folks need more serious acne treatment. Test your knowledge with this tretinoin quiz.
How much do you know about how car engines work? And how much do you know about how the English language works? And what about how guns work? How much do you know? Lucky for you, HowStuffWorks is about more than providing great answers about how the world works. We are also here to bring joy to your day with fun quizzes, compelling photography and fascinating listicles. Some of our content is about how stuff works. Some is about how much you know about how stuff works. And some is just for fun! Because, well, did you know that having fun is an important part of how your brain works? Well, it is! So keep reading!