How Fevers Help Fevers can be uncomfortable, but the upside is that they are evidence of the body's attempt to heal. When a person develops an infection, a section of the brain called the hypothalamus recognizes a threat. The hypothalamus responds by increasing the body's temperature. Since both viruses and bacteria are temperature sensitive, this environment helps prevent them from multiplying. In addition, scientists have found evidence that fevers may increase the number of certain lymphocytes—white blood cells that are part of the immune system. Increased lymphocytes make the body more effective in destroying infected cells. Of course, this doesn't mean that high fevers don't warrant medical treatment. In fact, another reason that fevers are beneficial is that they serve as warning signs, indicating that something is amiss. What is the main, or central, idea of the passage?