Natural D-Hist is a blend of flavonoids, antioxidants, proteolytic enzymes and botanicals designed to provide support for seasonal challenges caused by common environmental allergens. Natural D-Hist includes quercetin, a powerful flavonoid, that has been used in herbal medicine to help protect blood vessels. Bromelain enhances the absorption of quercetin, while stinging nettle leaf balances the hyper-immune response. This powerful combination actively promotes healthy nasal and sinus passages for individuals with elevated histamine and respiratory irritation.