Hello. There are innumerable skin issues that exist ranging from infections to eczemas to autoimmune diseases. Not all are due to low immunity but you may say altered immunity of skin. In general citrus foods and green leafy vegetables are loaded with vitamin C and antioxidants, which help. Protein rich diet is also advisable. In general you can curb on high glycemic foods like sugar and refined wheat flour. Dairy is to be restricted in acne. So it is a vast subject, what is actually your skin issue is to be known to give you some fruitful advice.