Is B12 useful for allergy?

The context does not address B12 for allergies. Generally, evidence for vitamin B12 as an allergy treatment is weak. Some mechanistic hypotheses suggest B12 may influence histamine metabolism, but human studies are lacking or inconclusive. B12 deficiency can cause symptoms like fatigue or neurological issues, but not typical allergy symptoms. There is no strong evidence that B12 supplementation helps allergic rhinitis, asthma, or food allergies. A few small studies on urticaria show mixed results. Caveat: B12 is safe in normal doses, but high doses are unnecessary without deficiency. For allergy management, standard treatments (antihistamines, avoidance, immunotherapy) are evidence-based. Evidence: unclear.