Caffeine is the chief stimulant in beverages such as coffee and tea. It’s often included in skincare products with claims that it will improve the look of cellulite or puffy eyes. Unfortunately, research into caffeine’s effects in this regard are mixed. Caffeine’s popularity in products related to cellulite is due to its distant relationship to aminophylline (an ingredient once thought to improve the look of cellulite), which is a modified form of theophylline, and caffeine contains theophylline.
Applied to skin, caffeine may have soothing and antioxidant properties, especially when skin is exposed to UV light. It can penetrate skin and has a constricting effect, which can help improve the look of redness but also may be sensitizing.
When it comes to puffy eyes, there is no research indicating caffeine can have any benefit; in fact, research has shown caffeine has an inhibitory action on a key protein in skin that helps it look younger. Truly, it’s a mix of pros and cons for skin, though lower amounts (less than 1%) in skincare products probably don’t present much, if any, risk.
References for this information:
Drug Design, Development, and Therapy, October 2014, pages 19,923-1,928
Skin Pharmacology and Physiology, 2013, issue 1, pages 8-14
British Journal of Clinical Pharmacology, August 2009, pages 181-186
The Journal of Clinical and Aesthetic Dermatology, January 2009, pages 36-40
BMC Complementary and Alternative Medicine, March 2006, issue 9, page 17
Bioscience, Biotechnology, and Biochemistry, November 2005, issue 11, pages 2219-2223