Common ingredients in brightening serums include Vitamin C, alpha arbutin, niacinamide, kojic acid, and hyaluronic acid. These ingredients work by reducing dark spots, inhibiting melanin production, improving skin texture, and providing hydration for a radiant and even skin tone. Other notable ingredients often found in brightening serums are azelaic acid, glycolic acid, and salicylic acid which help exfoliate and promote cell turnover for smoother skin.