Xylitol is present in many fruits and vegetables. It is contained in berries, oats, mushrooms, corn husks, sugarcane bagasse, and birch. Xylitol used in commercial products can be extracted from various hardwoods including birch, or corn cobs. It is produced by hydrogenation of xylose, a sugar aldehyde into a primary alcohol. In addition to its use as a sweetener, it is found in many other products including nose sprays.
Birch pollen contains a number of allergens, the major ones are known as Bet v1 and Bet v2. These substances are profilins, and are not structurally related to xylitol. In addition, I could find no history of allergic reactions to xylitol which would indicate any concern about a birch pollen-allergic patient about using xylitol.
In summary, there is no evidence whatsoever that a birch pollen-allergic patient cannot take xylitol.
Thank you again for your inquiry and we hope this response is helpful to you.
Phil Lieberman, M.D.