Thioctic Acid

Alpha-Lipoic Acid (ALA) is a great antioxidant that's also part of the body's natural antioxidant system. It's soluble both in water-rich and lipid-rich environments so it's versatile and can interact with many types of evil oxidants as well as other nice antioxidants. 

ALA seems to be a great choice for topical use as studies show it can penetrate the skin rapidly where it's converted to DHLA (dihydrolipoic acid), an even more potent antioxidant molecule.  A designed 12-week study from 2003 confirmed that 5% ALA cream can decrease skin roughness and improve general signs of photoagingstatistically significantly.

• References

  Beitner, Harry. "Randomized, placebo‐controlled, double blind study on the clinical efficacy of a cream containing 5% α‐lipoic acid related to photoageing of facial skin." British Journal of Dermatology 149.4 (2003): 841-849.

  Podda, Maurizio, et al. "Activity of alpha-lipoic acid in the protection against oxidative stress in skin." Oxidants and antioxidants in cutaneous biology. Vol. 29. Karger Publishers, 2001. 43-51.