Bacterial acne is one of the most common causes of blemishes for those in their 20s and 30s. How can you tell if your acne is bacterial? Ask yourself if anything dirty has come in contact with your face. Dirty face masks, pillowcases, scarves, cellphones, makeup brushes, and unwashed fingertips when applying skincare or makeup could all be culprits here. Thankfully, prevention of bacterial acne is reasonably straightforward: Regular washing of everything that touches your face.