November is a good time to discuss the immune system—and how to keep yours running at its best through all that potentially germy holiday season. Your immune system is your body’s defense system against health threats, such as bacteria, viruses, and other harmful substances. When your immune system needs to fight a threat, your body mounts an immune response—for example, mucus in your nose or a cough—designed to keep out invading microbes. To stay healthy, you want your immune system to be healthy, too. Abiding by good-health guidelines is a great way to care for your immune system. For example, eating a diet high in fruits and vegetables, not smoking, exercising regularly, getting adequate sleep, doing what you can to minimize stress, drinking only in moderation, and maintaining a healthy weight. You can help your immune system further by taking steps to avoid getting sick. Two seemingly easy, yet important, steps you can take are to wash your hands often, and don’t touch your nose and mouth with unwashed hands.