This TruSkin Naturals Vitamin C Serum ($20) is a grows in popularity with each day — it's currently up 120 percent in sales. According to the brand, the serum is "proven to reduce the appearance of wrinkles and fine lines while helping boost collagen, fade sun and age spots, improve skin firming, brightening, and tone for a smoother, fresher, more revitalized youthful complexion.