The ancient magnets are different from today's magnets. Few people eat magnets now. The so-called magnetic therapy is an attempt to treat diseases by using magnetic fields. Some magnetic fields are constant, while others are variable. According to Faraday's law of electromagnetic induction, changing magnetic field will produce electric field, which will affect nerve cells and muscle cells. This kind of influence is good and bad. If the magnetic field intensity is too large, it is likely to have a negative impact on health.