Cranberries are the fruit of the Vaccinium macrocarpon plant.
Its most studied components are its phenolic compounds: anthocyanidins and proanthocyanidins (PACs). Multiple recent scientific studies have shown that the cranberry PACs are capable of inhibiting the adherence of pathogenic bacteria to the surface of the urinary tract. Numerous studies in scientific literature attribute urinary tract infection preventive properties to cranberries.

Urinary tract infection is the inflammatory response of the urinary tract epithelium to a bacterial invasion. The most frequent is the infection of the bladder (cystitis) causing discomfort such as pain or stinging when urinating, pollakiuria (frequent urination of small quantities), tenesmus (feeling that the bladder has not been completely emptied) and, sometimes, haematuria (blood in urine). Urine may also have a strong odour and a cloudy appearance, there may be cramps in the suprapubic or low back region and, sometimes, low-grade fever (less than 38 degrees centigrade).