The career of lysine among dietary supplements began when it was discovered that it inhibits the reproduction of the herpes simplex virus both in-vitro (in a test tube) and in-vivo (in living beings). The herpes simplex virus (HSV) invades the nervous system and can reproduce there. Whoever gets it once is forced to live with it for the rest of his life, there is currently no way to completely destroy it. It hides in the body for a long time and is reactivated by fever, weakened states, stress, sunlight, menstruation, food, exposure to mercury during dental treatments, or viral infection. The prevalence of HSV-1 type in society increases with age, in the 30-year-old age group in the USA it is 50% among the wealthy, and 80% among the lower class of the population. In Hungary, 80% of the population carries the virus, and according to estimates, 2,000,000 people regularly have symptoms. Another type of herpes simplex, HSV-2, is sexually transmitted, and the probability of infection increases with the number of sexual partners.