For more than a year and a half, there has been an unprecedented amount of talk about the immune system—in the press, with our health-care providers and even among family and friends. But other than a vague notion that our bodies have a goal of keeping us healthy, the immune system remains largely a mystery for many of us. Bottom Line Personal asked naturopathic physician Laurie Steelsmith, ND, LAc, to explain how the immune system works to fight off all kinds of infections…


Every day, our bodies are exposed to thousands of viruses, bacteria, parasites and other pathogens. Our immune system— the body’s natural defense against infection and illness—keeps those bugs from taking up residence and making us sick. This complex biological system includes two main branches that work in tandem—the innate immune system, which we are born with…and the adaptive immune system, which builds up as we move through life, developing defenses against germs.

A healthy immune system includes millions of white blood cells that defend against and disable foreign invaders and abnormal cells. Your bone marrow produces these cells, as does your thymus gland. Some types of white blood cells, including phagocytes, literally consume bacteria and other germs.

Other immune system cells create antibodies, proteins formed after initial exposure to a virus or bacteria that protect you the next time you encounter the same bug. This is why someone who contracts and recovers from COVID-19 has some protection against repeat infections. It’s also why many healthy people feel fine after their first shot of a twopart COVID-19 vaccine but temporarily develop fever, chills and body aches after the second shot—the immune system recognizes COVID and starts to attack it.

Lymph nodes are the watchdogs of the lymphatic system, an immune-supporting network of organs, tissues and vessels that circulate a fluid called lymph (which contains everything from proteins and minerals to precancerous cells and bacteria). The reason your lymph nodes sometimes grow swollen or tender is because they’re packed with white blood cells and act as filters for foreign invaders, preventing them from reaching the rest of the body. Lymph nodes near the area of infection typically will swell up because they are hosting white cells in their war against the foreign substance— bacteria or viruses, for example. There are lymph nodes all over the body, but clusters exist in the armpits, groin and neck, and they can easily be felt when you have an infection. If swollen lymph nodes are accompanied by other signs of illness—fever, sore throat and/ or congestion—a foreign invader that was able to sneak by the immune system has been recognized, and the immune system is mounting an attack.

The skin also serves as a physical barrier to keep harmful toxins out of the body. Another filter—the spleen—strains pathogens and abnormal cells from the blood. You can live without your spleen, but when someone loses this organ—due to an illness or accident, for example—he/ she is considered immunocompromised and is susceptible to everyday germs that most people can easily fight off. Mucus is yet another immune system player. The slimy substance that lines the inside of the nose traps bacteria and viruses as they try to sneak into the body.


A huge amount of your immune potential lives in the gut—70% to 80% of the body’s immune cells, in fact. Deep in the bowels of your body, a vast ecosystem of trillions of microorganisms and good and bad bacteria—known collectively as the gut microbiome—exists. Among the gut microbiome’s varied jobs: Engaging in a constant dialogue with the immune system…helping to detect foreign invaders… and mounting a proper defense when pathogens are detected.

Interesting: A 2021 BMJ Gut study looking at microbiome data from 27 recovering COVID- 19 patients found that, compared with healthy individuals, those with COVID-19 infection lacked certain strains of good gut bacteria, suggesting that microbiome health may influence the severity of COVID-19 infection.


Here are ways to help fortify your body’s natural defense system…

Eat a whole-foods diet. The foods you eat hold incredible sway over your ability to stave off infections…

Shoot for organic, whole foods, such as fresh fruits and vegetables, unprocessed grains and nuts.

Avoid red and processed meat. They cause inflammation, thanks to their high saturated-fat content. Inflammation is good when you need to fight off a bug, but unrelenting inflammation contributes to a dysregulated immune system and potential autoimmune disease, allergies, chronic pain and tissue dysfunction.

Eat a serving or two of probiotic- and prebiotic-rich foods a day. Probiotics are good-for-you bacteria—kefir, yogurt, sauerkraut, kimchee, miso, tempeh and Kombucha all are probiotic. Prebiotics are a type of indigestible fiber that serve as food for the probiotics—garlic, onions, leeks, Jerusalem artichokes, barley, bananas and flaxseeds.

Fiber is your friend…sugar is not. The former bumps up the immune system’s responsiveness, while too much of the latter suppresses it.

Move your body. Exercise can help flush bacteria out of the lungs, reducing the chances that you will develop a cold, flu or other respiratory illness, and it helps distribute white blood cells and antibodies throughout your body, boosting your immune system’s ability to identify and fight intruders. Also, by temporarily increasing body temperature, exercise may function similarly to a fever, helping the body fight any lurking infections. Recent finding: A 2021 Sports Medicine meta-analysis found that higher levels of regular exercise are associated with a 31% lower risk of acquiring an infectious disease. Aim for 150 minutes per week of moderateintensity aerobic exercise, including walking, running, cycling or dancing.

Work with your immune system… not against it. It’s common for people to use decongestants and fever reducers when they have a stuffy nose or other cold symptoms, but those symptoms mean that your immune system is doing its job. Decongestants dry up the mucous membranes, preventing them from flushing the virus from your body. Fever reducers—ibuprofen (Motrin, Advil), acetaminophen (Tylenol) and aspirin—inactivate the work being done by your immune system to raise your body temperature.

If you’re feeling unwell and your fever is below 104°F, support your body’s natural ability to fight off infection by feeding it warm liquids (tea, soup)…holding your head over a bowl of steaming water and eucalyptus oil for five minutes several times a day (put one or two drops of eucalyptus oil into a bowl with four cups of boiling water, then create a tent over your head with a towel while you inhale)…and taking immune-enhancing supplements and herbs such as zinc (15 mg/day)…vitamin E (40 IU/day)…vitamin C (1,000 mg/day)…and quercetin (500 mg/day). Note: For temperatures of 104°F or above, seek medical attention.

Try dry brushing. Using a soft shower brush or loofah, lightly stroke your dry skin, always brushing toward the heart. This encourages the healthy flow of blood and lymph throughout the body, stimulates detoxification and removes dead skin cells for overall skin health. Try this technique once a day. Afterward, rub your skin with three drops of essential oil of cedar wood diluted in one tablespoon of jojoba oil.

Use antibiotics judiciously and only for bacterial infections. They don’t work on viral infections and can do more harm than good.

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