Nicotinic acid, also known as niacin, belongs to the water-soluble vitamin B3 family. Nicotinic acid and niacinamide are not the same substance; they are homologous derivatives with similar structures. Nicotinic acid contains a carboxylic acid group, making it more acidic and more likely to cause skin redness, stinging, and other irritations when applied topically. It is mostly used in oral nutritional supplements and industrial raw materials. Niacinamide, on the other hand, is milder, more stable, and less irritating. It is commonly used in skincare to repair skin and regulate oil production. After ingestion, nicotinic acid can be naturally converted into niacinamide in the body, both participating in the body's energy metabolism.