Optional additives include xylitol which is claimed to draw water into the sinus regions and helps displace bacteria.[21] Xylitol is commonly used to prevent acute otitis media in Europe and dental cavities in the United States,[22] but research into xylitol use in the sinus cavities is lacking. Another nasal irrigation additive is aloe extract, which helps to prevent nasal dryness. Sodium citrate and citric acid help not only to balance the pH, but also to improve the sense of smell.