What Causes Pimples To Leave The Scars Behind?

1. What causes pimples to leave red marks behind? When I was 15 (this was a long time ago), I had a lot of acne, because my mother did not believe in using a cleanser, so I never always washed my face with just water even though I occasionally wore foundation. I soon realized that cleansers are necessary and started using a 10% benzole peroxide cleanser. My acne cleared within a week, and I only had a pimple every few months. Six months later, I got a very large pimple that was actually painful (I never had painful pimples before). It took 3 weeks to heal, a long time for me because my pimples usually heal within 4 days, and after it was gone, it left a red mark that was gone after 6 months. Ever since, even though I rarely have acne, 40% of them leave red marks.