Penicillin used to be administered without allergy now allergy may be due to different manufacturers as well as different physical qualities of individuals and other reasons. Penicillin production process is different, there may be allergies, in the hospital with the same manufacturer to switch to a different batch number of penicillin, will also do the skin test. There is also a relationship with personal physical fitness. Allergy occurs because the combination of antigen and antibody produces an immune response. Since penicillin has been used before, penicillin can be used as a semi-antigen, and after entering the body, it becomes a complete antigen, and then anti-penicillin antibodies are produced. When penicillin is used again, an allergic reaction may occur. The purity of the drug may also cause an allergic reaction. If you experience any discomfort during the use of the drug, you should seek medical attention.