Adults generally have difficulty getting HFMD, and even when they do, the symptoms are generally not severe. The reason why it is difficult for adults to get HFMD is probably because adults have already been exposed to most of the viruses that can cause HFMD when they were small, and they had an illness or an insidious infection when they were small, without any symptoms, so the body has already acquired the relevant immunity, and when they are infected with the relevant viruses as adults, these viruses are likely to have been exposed in the past, so the immune system can The immune system is able to recognize them quickly and clear them out of the body. It is likely that some of the viruses were not exposed when they were young, and when they are re-exposed at this time, they may still develop and when infected can cause symptoms of HFMD. In addition, some of the viruses that cause HFMD are likely to mutate. After the mutation, the body’s immune system does not recognize it, and when infected at this time, the immune system is not able to remove them in time, which can also lead to symptoms of HFMD.