This can be good or bad, depending on several factors like A) the amount of acne or pimples on your face, B) whether you've washed your face before hand, and C) whether or not your skin is sensitive. Lemons contain citrus, which is a type of acid that can eat into your skin if you're not careful. If you rub lemon juice on your face more than once or twice a week, it can start stinging and open up wounds on your face. However, if you do it minimally and make sure to wash your face before and afterwards, it can eat away the acne and pimples. Just make sure you don't do it too much, as it can also eat PAST that.