First developed to treat acne, retinoids, or retinols, are chemical derivatives of vitamin A that can smooth out fine facial lines. They help thicken both the epidermis and dermis, exfoliate dead skin cells, speed the turnover of keratinocytes and increase production of collagen and hyaluronic acid, a carbohydrate that occurs naturally in the body and serves as a lubricant for joints, muscles and skin. But retinoids also increase something else: the skin’s sensitivity to the sun. Use them at night for optimal benefit.
维生素A酸最早是用于治疗粉刺的，它是维生素A的一种化学衍生物，可以平复我们脸上轻微的表情纹。它有助于增加表皮层和真皮层的厚度，去除死去的皮肤细胞，加速角质细胞的新陈代谢，促进胶原蛋白和透明质酸的生成，透明质酸是一种体内自然生成的碳水化合物，是关节、肌肉和皮肤的润滑剂。但维生素A酸也有副作用：会增加皮肤对日光的敏感度，所以最好是在晚上使用。