My son SWCAH had acne on his back, same age, we went to see a dermatologist.  She said it was steroid induced acne and not the scarring type, it was caused through dex.  We changed to hydrocortisone and he started treatment for his back, which cleared up, and he no longer gets acne type spots.  There is treatment for acne, and it is successful.  His back was a real mess and it took almost 18 months for the marks to disappear which they have. Yes, with CAH one is on replacement doses, but it does not mimic the normal rhythm of the body’s natural cortisol production, so there will be side effects. Best to get a specialist to look and then you will know what you are dealing with.