You are constantly using your immune system, though you probably take it for granted. However, as soon as it starts slipping and you catch a cold, walking to work can feel like climbing a mountain. And no matter how much makeup you put on, you may not be able to erase those dark circles under your eyes.So what is the immune system? It’s your body’s bodyguard. It kicks in when it senses bacteria, viruses and other invaders. Your hand alone has around 200 million germs on it, so it’s likely your body is infected right now, and your cells are currently working to fight off germs!The immune system has a wide range of solutions, making it quite complex. Let’s look at a common example of bacteria: staphylococcus, which causes pimples. When your body spots this intruder, white blood cells (macrophage) engulf and digest it. Corny as it sounds, your immune system acts like a guard that uses its walkie talkie for back-up from other cells. The cells travel through the bloodstream (which is why scabs become red, from the excess blood supply).QUIZ: How Healthy Do You Feel?The macrophage takes in information about the foreign cells so the immune system recognizes it. This essentially puts the bacteria on your body’s most wanted list. The back-up immune cells look for the code (mug shot) to ID and destroy the bacteria. T cells attack and digest the bacteria. B cells create immunoglobulins, acting like bullets to blast through the bacteria covering.Lastly, the battle leaves the bacteria dead, and also kills B and T cells. This leaves a pool of waste. The B and T cells self-destruct so they don’t destroy healthy cells, it’s called apoptosis. The waste pool builds pressure under the skin, creating redness from new blood supply lines coming to battle. That yucky pus comes from white blood cells responding to the scene. Like a volcano, waste material rises to the surface to create the notorious pimple.So that’s how the immune system is supposed to work, but it doesn’t always run smoothly. There are different levels of immune threats, and various ways your system reacts to these threats. If you don’t take care of your body, your immune system will become less effective as you get older.With age, your identification system becomes full and some of the older info gets deleted so you have space for information on recent intruders. Your B cells slow down or malfunction, leaving you less able to fight bacteria, as you age. There are also crooked cops in your immune system—these cells seek and destroy some good cells instead of only bad ones.