Acetaldehyde is a highly toxic and mutagenic product of alcohol fermentation and metabolism which has been classified as a Class I carcinogen for humans by the International Agency for Research on Cancer of the WHO. Many Candida species representing oral microbiota have been shown to be capable of marked acetaldehyde production. The aim of this study was to examine the effects of various sugar alcohols and sugars on microbial acetaldehyde production. The study hypothesis was that xylitol could reduce the amount of acetaldehyde produced by Candida. Laboratory and clinical isolates of seven Candida species were selected for the study. The isolates were incubated in 12 mM ethanol and 110 mM glucose, fructose or xylitol at 37 °C for 30 min and the formed acetaldehyde was measured by gas chromatography. Xylitol significantly (P<0.0001) reduced the amount of acetaldehyde produced from ethanol by 84%. In the absence of xylitol the mean acetaldehyde production in ethanol incubation was 220.5 μM and in ethanol-xylitol incubation 32.8 μM. This was found to be mediated by inhibition of the ADH enzyme activity. Co-incubation with glucose reduced the amount of produced acetaldehyde by 23% and co-incubation with fructose by 29%. At concentrations that are representative of those found in the oral cavity during the intake of proprietary xylitol products, xylitol was found to reduce the production of carcinogenic acetaldehyde from ethanol by Candida below the mutagenic level of 40-100 μM.