Does contact with allergic materials cause immediate reactions?

To each his own! It really depends on you. Based on how your immune system responds to the potential allergens determines what type of reaction if any occurs. For your neighbor, it may take one exposure while for you it might take 10 or more. It depends on your body’s sensitivity. Typically, however, reactions can occur in one or two days initially, but if you have been exposed before and the antibody is ready, then your body reacts faster.