Hello Thank You for contacting HCM. B12 as no such role in allergic response. I would suggest you following things for recurrent allergic problem: Take levocetirizine one if there is insect bite Take montelukast one daily for one month. Research has shown that it decreases the allergic symptoms considerably. I would also suggest you to under go allergy testing at allergy clinic as you have chronic allergy problem. It will tell that you are allergic to what specific thing. The results will help an allergist to prescribe you immunotherapy to that specific allergen and it will improve the problem. Hope this answers your question. If you have additional questions or follow up questions then please do not hesitate in writing to us. Wishing you good health.