How much do we really know about our favorite cosmeceutical ingredients?

To date, we are unaware of a review that has investigated common cosmeceutical ingredients in order to answer the three specific questions proposed by the father of cosmeceuticals, Dr. Albert Kligman. It is the goal of this review to gather all the published scientific data on five common cosmeceutical ingredients, answer the three major questions about the scientific rationale for their use, and ascertain how much we really know about consumers' favorite cosmeceutical ingredients.Most of the research concerning cosmeceutical retinoid ingredients is based upon the effects of retinoic acid on the skin. Clinical trials concerning retinol and retinaldehyde are scant and lacking in statistical evaluation for significance. There is research substantiating the effects of kinetin in plants and also in-vitro antioxidant effects. However, proof of anti-aging activity remains elusive, and the clinical efficacy of kinetin is based on limited data. Niacinamide is the ingredient investigated that most closely upholds the "Kligman standards" of cosmeceutical-ingredient analysis. With the available scientific evidence on topical niacinamide, clinicians are able to adequately answer questions about permeability, mechanism, and clinical effect. Both green tea and soy have been popularized commercially based on their antioxidant effects, yet there is a paucity of clinical studies concerning their efficacy as topical anti-aging agents. It may be that soy and green tea are better at preventing the signs and symptoms of skin aging than actually reversing them. Since cosmeceutical products are claiming to therapeutically affect the structure and function of the skin, it is rational and necessary to hold them to specified scientific standards that substantiate efficacy claims.