Hi there, there are many factors which lead to acne, and hormones maybe one of the top causes. If your skin doesn’t show any signs of irritation before, it could be hormonal change in your body. Sometimes, it’s really hard to figure out the cause. However, we suspect the root of issue being the cosrx instead of hormones as you started breaking out after introducing it to your routine. Since it’s the only change you made, I would strongly recommend to stop using the product and patch test it again after a few days. We can’t say for sure what maybe the cause, it maybe the acids or the formulation is just not suitable for your skin. If you were to filter the cosrx toner review into one to two stars, you’ll see many facing the same issues.