Fructooligosaccharides

Short chains of fructose, usually three to five units, made enzymatically from sugar beet or cane sucrose. The same molecule is sold as a gut prebiotic and appears that way in CULTURE; in SWEEP it is dissolved in the water phase of a toner and never gets past the skin's surface.

Skin is a poor place to be a bacterium — dry, salty and short of food — and what grows there is partly decided by who can use the available carbon. In culture, short-chain FOS is a sugar that Staphylococcus epidermidis, the standard commensal, grows well on, while Cutibacterium acnes and Staphylococcus aureus use it poorly, so the balance tips. That is a clean result in a dish. The gap between that dish and your chest is wide: nobody has established what concentration actually survives on skin once a toner dries, how long it stays before the next shower, or whether a shift measured over 24 hours in a well plate means anything over weeks on a person. The humectant half is simpler and not in dispute — small sugars bind water and hold it in the stratum corneum, which is a physical effect you can feel within minutes.

Binds water in the top layer of skin as a humectant, and in laboratory models is preferentially used by friendly skin bacteria. Studied for supporting the normal skin microbiome.

Anyone using a body toner on chest, shoulders and back — which is everyone using SWEEP, since it is fixed in the formula. Not for broken, raw or freshly shaved-sore skin, not for the eye area, and not for anyone looking for a treatment for a diagnosed skin condition, which this is not.

Onto clean, still-damp skin after a shower, across the areas you want covered. Follow with a moisturiser if you run dry — a humectant on its own can pull water out of skin in dry air with nothing to seal it in. If you already use a strong acid on your chest, do not start both in the same week.

Skin that feels hydrated and smoother to the hand within minutes; that is the humectant and the glycerin, and it is real. The microbiome half is invisible — you cannot see it, feel it or measure it at home, and you should not expect to. Anything you notice in the mirror over a fortnight is water and the gluconolactone, not bacteria changing sides.

The key skin paper is Le Bourgot and colleagues, Scientific Reports, 2022 (doi 10.1038/s41598-022-13093-5): sugar-beet short-chain FOS of degree of polymerisation 3–5 promoted and sustained Staphylococcus epidermidis growth to 24 hours in minimal medium while inhibiting Cutibacterium acnes and Staphylococcus aureus, and 1% scFOS shifted the competition in favour of S. epidermidis with respect to C. acnes on a reconstructed human epithelium model. In vitro from start to finish, and four of the seven authors are employed by Tereos, which manufactures the ingredient. A 2025 review of prebiotic oligosaccharides in skin health (Zeng and colleagues, Antioxidants 14:754) surveys the wider field and flags structure/function relationships and clinical scalability as still-open problems. For contrast, the eaten side is properly mapped: Bouhnik and colleagues (Journal of Nutrition, 1999) gave 0, 2.5, 5, 10 or 20 g a day of scFOS to 40 healthy volunteers for seven days and found faecal bifidobacteria significantly raised at 10 and 20 g — not at 2.5 or 5 g — with a dose–response correlation and excess flatus at 20 g, concluding 10 g a day was the optimal well-tolerated dose. Not supported: any claim that topical FOS treats acne, eczema or folliculitis, that it repairs a damaged barrier by acting on bacteria, or that the eaten dose-response applies to a toner.