Nettle (Urtica dioica) has a long history of traditional use for treating respiratory allergies, such as hay fever (allergic rhinitis). More recently, scientific interest has focused on its potential anti-inflammatory and antihistamine properties. Laboratory studies have shown that nettle extracts can inhibit key inflammatory pathways and reduce the production of histamine, the chemical responsible for many allergy symptoms. For example, in vitro experiments demonstrate that nettle may block histamine receptors and inhibit prostaglandin formation, both of which are relevant to the allergic response.

Several small clinical trials have evaluated nettle for seasonal allergies. One double-blind study found that freeze-dried nettle modestly improved symptoms compared to placebo, but the effect size was not large and the study sample was small. Other studies have been inconclusive or have failed to show significant benefits. Overall, while laboratory and preliminary clinical data are promising, the clinical evidence remains limited and inconsistent, and larger, high-quality randomized controlled trials are needed to confirm nettle’s effectiveness for respiratory allergies.

In summary, nettle’s use for respiratory allergies is supported by both traditional use and a growing but still preliminary body of scientific research, justifying a moderate evidence rating of 2 out of 5.