Dr Phil Kieran: My teen has severe acne — cutting out fast food and sugar has made little difference

The causes of acne are complex. They include changes in the interplay of the oil glands in the skin (frequently affected by changing levels of testosterone), imbalances in the bacteria present on the skin, and changes in the immune system

Dr Phil Kieran: Acne varies from mild (less than 30 lesions), involving only one area of skin with small lesions and no scarring, to severe (over 125 lesions), with prominent inflamed pustules or cyst-like lesions on multiple body areas and scarring. Treatment plans will vary depending on the severity and type of acne.

My teenage son has severe acne on his back. Some of the spots are more like cysts and can be very painful. He has changed his diet, cutting out fast food and sugar, but it has made little difference. It's beginning to affect his mood. What would you recommend?

Usually, I advise on self-management before telling people to see their doctor. However, in this case, it sounds like you have already tried several things, and they haven’t worked, so medical intervention is likely necessary.