Take vitamin C supplements when you feel a cold coming on? The problem is, you can’t actually “strengthen” your immune system, says Dr. Jen Gunter. Diving into the elegant network of cells, tissues and organs that protect us every day, she introduces two kinds of immunity that specialize in recognizing and fighting off bad bacteria, viruses, fungi and toxins — and shares what you can do to keep your immune system healthy. Want to hear more from Dr. Gunter? Check out her podcast Body Stuff, from the TED Audio Collective.