When humans moved northwards, less sun started hitting their skins, and this meant a lack of Vitamin D that comes in from the Sunlight. And to allow that to happen, the skin had to shed color and turn white, and this came with so many problems. Acne is one of them.
People develop acne naturally in their teens, and carry it on later into their adulthood, or they acquire it when they use ammonia based products. People say fight chemicals with chemicals, but i wouldn’t recommend this for acne caused due to ammonia. I would recommend only all natural acne products to do the trick and make acne vanish away from your skin for ever.