Some in vitro evidence has found that quercetin can stabilize mast cells (which release histamine during allergic reactions) and inhibit the inflammatory pathways associated with allergic diseases like allergic rhinitis.[1] However, human research is scarce.
There is one randomized controlled trial that found some benefit in improving symptoms of allergic rhinitis, but this has yet to be confirmed in other trials.[2]
Overall, quercetin might help with allergies, but more research is needed to determine how effective it truly is.