How long to use azelaic acid will have effect varies from person to person, and the severity of the disease has a certain relationship, the general use of 6 to 15 days will show results. 1. Azelaic acid is a kind of acidic substance, can play the role of killing epidermal staphylococcus and propionibacterium acnes, can inhibit the skin oil secretion, when the face has acne or growth of chloasma, freckles, sun spots, and other spots, you can use azelaic acid to carry out the treatment. You need to clean your skin before use, and then apply the drug to the acne or spots for massage to promote the absorption of the drug. 2. How long to use azelaic acid will be effective varies from person to person, and the specific severity of the disease has a certain relationship. If the condition is mild, you can see the effect in about 6 days, if the condition is too serious, it will take about 15 days to see the effect. It is recommended that patients use azelaic acid for treatment under the guidance of a professional doctor, do not blindly use the drug on their own to avoid adverse reactions.