Numbuzin No. 5 refers to the Numbuzin No. 5+ Vitamin Concentrated Serum (or Goodbye Blemish Serum), a popular Korean skincare serum focused on brightening, fading dark spots, and evening skin tone using potent ingredients like glutathione, niacinamide, Vitamin C derivatives, and alpha-arbutin. It’s known for its fast-absorbing, lightweight formula that targets hyperpigmentation and post-acne marks, providing antioxidant protection and hydration for a radiant, smoother complexion.