"As a nurse, I've tried many products and look for ingredients shown to work in clinical research.The glycolic acid allows the hydroquinone to penetrate skin cells and work better(GENIOUS!)...You won't get this in cheaper over-the-counter products.This is THE BEST depigmentation agent available. It's high potency glycolic acid also exfoliates and makes skin smooth, even, and nearly glow after a week of consistent use. However, be warned to avoid the sun or brown spots will worsen and not resolve.You must avoid sun and wear sunscreen. PS, This also helps old acne scars!"