Summer 2020 • Vol. 26 • Issue 6
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Caffeine—A Widely Used Topical Ingredient in Personal Care Products with Numerous Claims for Activity in Skin …by Paul Thau
affeine is the most widely used drug in the world. Its use in skin care products has existed for a range of applications for many years; however, based upon emerging knowledge about the influence of caffeine on skin biochemistry, there has been renewed rationale and justification for the use of caffeine and its derivatives for these applications. Further, advanced delivery systems to enhance performance are now available. This review covers information from scientific literature and patent information related to caffeine’s chemistry, applications, and methods to enhance its topical delivery and efficacy.
Chemistry
Caffeine is synthesized in plants from the purine nucleotides, adenosine monophosphate, guanosine monophosphate, and inosinic acid. These in turn are transformed into xanthosine, and then theobromine, which is the next to last precursor of caffeine. Being readily available as a byproduct of the coffee decaffeination process, caffeine is generally not commercially produced by chemical synthesis. Pure anhydrous caffeine is a white colorless powder having a melting point of 237–238 °C. Caffeine is moderately soluble in water (2 g/100 mL) and very soluble in ethanol (15 g/100 mL). It is weakly basic (pKa = ~0.6) requiring strong acid to protonate it. However, it does not form stable salts of strong acids, since they are hydrolyzed readily in water. The solubility of caffeine in water increases in the presence of organic acids or their alkali salts (e.g., benzoates, citrates, or salicylates). Monographs for caffeine citrate and caffeine sodium benzoate are included in the U.S. Pharmacopeia.
Figure 1. The molecular structure of caffeine. Pharmacological Activity of Caffeine
Caffeine is naturally produced by several plants and is found in coffee beans, guarana, cacao beans, and tea. In nature, caffeine acts as a natural pesticide. It paralyzes and kills insects that attempt to feed on the plants. Its pharmacological activities include cardiac and respiratory stimulation and promotion of kidney diuresis. The therapeutic dose of caffeine is about the same as the amount found in an average cup of coffee, between 100 and 200 milligrams. (continued on Page 4)
SKIN MICROBIOME: PERSPECTIVES ON AGING, COMPROMISED SKIN AND COSMETICS NYSCC Programs...see page 6 for more information.