Your immune system is a complex network made up of an array of cells and biological compounds that work together to keep you healthy as your body comes into contact with foreign “invaders” of all sorts—bacteria, viruses, fungi, allergens, toxins, and more. Your immune system is tasked with identifying harmful substances and getting rid of them all while letting benign substances, like food and good bacteria, pass through the body naturally. You probably don’t even think about your immune system until you get sick, but here are 5 surprising facts about your immune system that you can use to help stay healthy.

#1 80 Percent of Your Immune System Is in Your Gut
Your immune system is housed largely within your lymphatic system, which is a network of vessels and glands found throughout most of your body and concentrated in and around your gut—in the gut-associated lymphoid tissue (GALT). It may sound strange at first, but when you think about how much food passes through your digestive system—and that food carries microbes, potential allergens, and toxins into the body—it makes sense that your immune system would be concentrated in your gut.

The immune system in your gut is hard at work identifying those substances and organisms that must not enter the body so that nutrients can be absorbed and good bacteria can set up shop in your gut to keep you healthy. If you continually eat foods that your immune system identifies as harmful—or foods that feed harmful bacteria in your gut—you’ll throw off your immune balance and be prone to illness. Likewise, if you don’t support your gut bacterial balance by replenishing the good bacteria, your immune system won’t receive the right messages and will mount an immune response against seemingly benign substances like foods and even your own body.

#2 Inflammation Is Your Immune System’s First Responder

When your immune system encounters a substance it identifies as a foreign invader, the first responders, so to speak, are those cells and biological compounds involved in the process of inflammation. The inflammatory response is a rapid, somewhat messy reaction that destroys almost everything in its path, including healthy cells and tissue, in order to destroy the perceived foreign invader. While this process can be life-saving, when inflammation is chronic, healthy tissues become damaged and disease can set in. A healthy immune response involves a rapid inflammation response that resolves soon after it begins.

 #3 A Fever Means Your Immune System is Working

When your immune system encounters a viral or bacterial infection that requires a strong immune response, it may need to raise your body temperature to effectively eliminate the organism, which has a difficult time surviving at higher temperatures. So if your first response to a fever is to take fever-reducing medication, you may not actually be helping fight your illness. Talk with your doctor about when such medication is necessary, and when you can withstand a fever to help your immune system work as it is designed.

#4 Avoiding All Germs Is Not Good for Your Immune System

Getting sick does not necessarily mean that your immune system is impaired. In fact, coming into contact with certain microbes actually helps prime your immune system so that it responds better to future encounters with microbes. It’s how you build stronger immunity. If you rarely come into contact with germs, your body will have a hard time mounting a response against them once you do encounter them, and you may get even sicker than you would have if your immune system had already fought a similar illness or come into contact with a variety of microbes.

This concept is known as the hygiene hypothesis, an idea that emerged from research comparing children raised in ultra-sanitized environments to children raised in environments rich in microbes. Those children raised in ultra-sanitized environments have higher rates of allergenic illnesses like asthma, eczema, and allergies (all of which involve an imbalanced immune response).

#5 Vitamin D is Your Immune System’s Best Friend

Most people think of vitamin D as a bone-building nutrient, and they’re not wrong. But vitamin D plays many important roles in the body. One of vitamin D’s superpowers is to help balance immunity. If you haven’t checked your vitamin D level yet, ask your doctor to do so at your next visit. Most people need more than the daily recommended amount to maintain a healthy vitamin D level. If you get sick often, your vitamin D level could be low. It’s worth checking.

Follow these five tips to keep your immune system working. Follow a healthy diet rich in fiber and vitamins. Here’s diet program I designed to keep your gut healthy