The scars on my arms as a child are from the cowpox vaccine or the BCG vaccine. Cowpox vaccine is also known as smallpox vaccine, and its main effect is to induce the body of the vaccinated person to produce specific antibodies to prevent smallpox virus infection. Generally, 3 days after vaccination, a red papule will appear at the location of vaccination, the papule will form a herpes in about 5 days, it will turn into a pustule in about 8 days, a brown scab will form in about 12 days, and the scab will fall off and leave a scar in about 18 days. BCG is a live attenuated vaccine, which can enhance macrophage activity and bactericidal ability after vaccination, and can greatly reduce the incidence of tuberculosis and meningitis in children. About 2 weeks after BCG vaccination, small bumps will appear, and then gradually increase in size, 4~8 weeks will form pustules or broken, in 10~12 weeks will start to scab, after scabbing will leave a small reddish scar.