Why Adding Coffee Makes Better Soap
What Coffee Does to Soap.
We prefer domestic ingredients, but just love the coffee soap too much to stop making it. This is because Coffee gives soap better exfoliation, antioxidant, and odor-removing properties.
Exfoliation
Coffee grounds fall in the 420–707 micrometer particle size range, which a ScienceDirect study identifies as appropriate for body exfoliation without disrupting the skin barrier. A 2025 clinical trial in the Journal of Cosmetic Dermatology confirmed measurable efficacy from spent coffee ground formulations and found participants reported improved skin texture and feel.
Antioxidants
Coffee is one of the densest sources of polyphenols available. A study published in the International Journal of Dermatology found that coffee polyphenol consumption was statistically associated with fewer UV-induced pigmented spots, with chlorogenic acids identified as a likely contributing factor. A follow-up study published in Clinical, Cosmetic and Investigational Dermatology confirmed the finding across a larger cohort.
A double-blind, placebo-controlled clinical trial published in the Journal of Drugs in Dermatology found that a skincare system containing Coffea arabica applied twice daily reduced fine lines, improved skin texture, and was well-tolerated across 40 female participants. A separate peer-reviewed review in Cosmetics (MDPI) confirmed that topically applied chlorogenic acids from coffee by-products demonstrate antioxidant, anti-aging, and photoprotective activity. A study published in Scientific Reports further found that coffee pulp extract applied topically showed antioxidant, antimicrobial, and wound-healing properties in lab testing.
Disclosure: rinse-off contact time in a bar of soap is short and these studies involve leave-on formulations or consumption. Still, similar if less stark benefits still likely remain.
Odor Removal
Researchers at The City College of New York, publishing in the Journal of Hazardous Materials, found that the nitrogen in caffeine boosts carbon's ability to bind sulfur compounds through adsorption. The porous structure of roasted grounds gives odor molecules a surface to attach to, and the nitrogen reacts with the sulfur-based compounds responsible for the worst smells.
We've always tried to keep our ingredients domestic but coffee is the one thing we couldn't give up. Turns out there is evidence for our preference.