Cystic acne is caused by hormonal imbalances and toxicity in our body and it can start with an irritated stomach lining. Eating excess carbs can lead to all those conditions, and your skin can be in better condition on low carb than ever before.
Another thing that can cause breakouts is excessive cardio exercise that leaves your body acidic. That happens when you workout at high intensity and the lactic acid builds up in your body to toxic levels. Depending on the strength of your lymphatic and endocrine systems, this toxicity can take many days to clear out. Antioxidants like Vitamin C can help getting rid of cystic acne, but it is best to workout at lower intensities most of the time.