​How does acupuncture work for hay fever?

The short answer is that acupuncture affects the immune system and reduces the allergic inflammatory response to allergens, and therefore symptoms, and also improves people’s tolerance to would-be allergens
Acupuncture for allergic rhinitis is one of the many conditions that have been extensively studied by western medical science - in fact some studies have found acupuncture to be more effective than medication, and that symptoms continued to improve for up to 3 months after treatment. Acupuncture has also been recommended in the allergic rhinitis (hay fever) clinical practice guideline of the Otolaryngology Head Neck Surgery Foundation in the US as a treatment option for those who prefer a nonpharmacological treatment.