Azelaic acid is a very gentle leave-on exfoliant that helps unclog pores and refine skin's surface. Azelaic acid also significantly lessens factors in the skin that lead to sensitivity and bumps and delivers antioxidant benefits.  It has antimicrobial and anti-inflammatory properties. Research has shown that azelaic acid can significantly diminish the appearance of skin blemishes, help fade post-acne marks and other discolorations, refine skin’s surface, and reveal a more even skin tone. It can even reduce skin sensitivity and is compatible with any skin type. 
This is a liquid product to mix into products not a thick serum. 
Azelaic acid has proven to be an effective tyrosinase inhibitor. That means it prevents a process known as melanin synthesis, which is how your skin produces pigments that can vary your skin's tone. Its antibacterial effects go further by inhibiting the synthesis of the cellular protein in bacteria such as staphylococcus epidermis, and propionibacterium acne. It is used in the treatment of : Hyperpigmentation Sun spots & melasma  Rosacea  Acne scarring  Adding the 5% Azelaic Acid to your routine is easy: it can be applied once or twice daily after cleansing, toning, and exfoliating. Apply on its own or mix with your favorite serum or moisturizer. It's fine to apply it to the entire face, or you can target blemished areas as needed. During the day, finish with a broad-spectrum sunscreen rated SPF 30 or greater.  You should discontinue using azelaic acid if you develop the following side-effects: Burning and tingling of the skin Peeling where the acid was applied  Drying or reddening of the skin  It is recommended that you do a patch test to determine skin sensitivity and allergy.  Azelaic acid is much milder than alpha hydroxy acid, glycolic acid, salicylic acid or lactic acid. And because it is classed under Class B, which means that it is one of the few topical treatments that are safe to use during pregnancy and breastfeeding - women are leaning more on this gentle acid for treating rosacea and melasma during and after pregnancy.