Product Details (Formerly Natural D-Hist, an Ortho Molecular Product) Hista-D Essentials is the ideal solution for many of the 40 million Americans who anticipate seasonal changes. Formulated for maximum effectiveness, Natural D-Hist utilizes carefully selected natural components to provide optimal support for nasal and sinus passageways. Why These Natural Ingredients? Quercetin Naturally found in onions, quercetin supports mast cell stability and is a powerful natural flavonoid. Quercetin has been shown to promote sinus and respiratory health. Stinging Nettles Leaf Studies have shown stinging nettles to demonstrate positive support for nasal passageway function. While further study is needed, stinging nettles in supplementation demonstrated measurable support after only one week. Bromelain A strong pineapple enzyme, bromelain supports normal mucousal tissue function and enhances the absorption of quercetin. N-Acetyl L-Cysteine (NAC) An amino acid, NAC helps to promote the normal viscosity of mucus. Studies have shown individuals have been supplemented appropriately without side effects when given NAC.