Alkaloid found in coffee, tea, and kola nuts. Caffeine is the chief stimulant in beverages such as coffee and tea. It’s often included in skin-care products with claims that it will reduce cellulite or puffy eyes. Unfortunately, caffeine’s results in this regard are mixed.
Caffeine and its constituents are thought to convey antioxidant benefits when consumed orally. Studies have looked at oral consumption of caffeine-containing beverages followed by exposure to UVB light (the kind that causes sunburn and skin tumors) and found that compared with those who drank decaffeinated beverages, the drinks with caffeine conveyed a protective benefit (Sources: Journal of Investigative Dermatology, July 2009, pages 1,611–1,613; Photochemistry and Photobiology, March-April 2008, pages 330-338; and Carcinogenesis, August 2005, pages 1,465–1,472).
Applied to skin, caffeine may have anti-inflammatory properties (Source: Food Chemistry and Toxicology, September 2012, ePublication). It can penetrate skin’s barrier and has a constricting effect which can help reduce redness but may also be irritating. It’s not a slam dunk for facial redness, and in fact some may find it worsens the problem, but it’s worth experimenting with if you’re curious.
Caffeine’s popularity in products related to cellulite is due to its distant relationship to aminophylline (a pharmaceutical once thought to reduce cellulite), which is a modified form of theophylline (Source: Yale New Haven Health Library, Alternative/Complementary Medicine), and caffeine contains theophylline (Source: Progress in Neurobiology, December 2002, pages 377–392). There is no substantiated research proving theophylline can affect cellulite, but researchers have disproved aminophyilline’s claimed impact on cellulite.
Research on caffeine’s effect on cellulite when applied topically is mixed, and more recent studies were done on mice, not real women with cellulite. Although caffeine may play a role in reducing the size or number of fat cells, the appearance of cellulite is a combination of fat and skin’s structure, the latter of which caffeine cannot impact (Sources: Skin Pharmacology and Physiology, Volume 26, 2013, pages 8-14; and Journal of Cosmetic Dermatology, March 2008, pages 23-29).
When it comes to puffy eyes, there is no research indicating caffeine can have this benefit when applied topically. However, caffeine does have potential as an antioxidant, so it isn’t a wasted ingredient in skin-care products (Sources: BMC Complementary and Alternative Medicine, March 2006, http://www.biomedcentral.com/1472-6882/6/9; Bioscience, Biotechnology, and Biochemistry, November, 2005, pages 2219–2223; Obesity Research, July 2005, pages 1195–1204; and Sports Medicine, November 2001, pages 785–807).