There is some difference between azelaic acid and 15% azelaic acid, but there is also some connection. 15% azelaic acid belongs to azelaic acid, but azelaic acid does not necessarily mean 15% azelaic acid. Azelaic acid can be formulated in different concentrations, of which 15% azelaic acid is one, and azelaic acid can also be formulated in 10% and 20% concentrations. It is important to note that both azelaic acid and 15% azelaic acid have the same main ingredients. Azelaic acid has the ability to dissolve acne, antibacterial, anti-inflammatory and antioxidant properties, and is generally used to improve mild and moderate common acne, where 15% azelaic acid also inhibits the growth of melanin. Topical azelaic acid may cause local irritation such as redness, swelling and itching, which usually disappears on its own. It is recommended that patients who need to use azelaic acid choose the concentration under the guidance of a doctor and follow the doctor’s instructions for standardized treatment to avoid serious adverse reactions.