What is it? Also called niacin, it is one of eight water-soluble B vitamins. All B vitamins help the body to convert carbohydrates into glucose (sugar), which is burned to produce energy. What does it do? These B vitamins, often referred to as B-complex vitamins, are essential in the breakdown of fats and protein. B-complex vitamins also play an important role in maintaining muscle tone along the digestive tract and promote the health of the nervous system, skin, hair, eyes, mouth and liver. What is it used in? Niacin is used in skincare products as an anti-ageing agent and for the treatment of acne.