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What Is Your Immune System?

Medically Reviewed by Sabrina Felson, MD on October 19, 2019

You’ve heard of your immune system. But how much do you know about it?

There’s a good reason to find out. When you understand everything that it does for you, and how everyday things affect it, you can help it keep you well.

It Looks Out for You

Your immune system works to root out germs and other invaders that have no business in your body.

For example, if you inhale a cold virus through your nose, your immune system targets that virus and either stops it in its tracks or primes you to recover. It takes time to get over an infection, and sometimes you need medicine to help, but the immune system is the cornerstone of prevention and recovery.

It Likes It When You Relax

Do your best to tame your stress. When you’re wound up, your immune system doesn’t work as well as it does when you’re confident and mellow about your challenges. That may make you more likely to get sick.

Ongoing stress, such as being in a difficult relationship, living with a chronic disease, or being a caregiver, can take its toll on your immune system. Over time, it can make you more vulnerable to illnesses, from colds and flu to chronic diseases such as diabetes and heart disease. Chronic stress seems to age the immune system, studies show, making you more likely to get a cold or the flu, and to develop diabetes and heart disease.

Everyone goes through stress. What matters is how you handle it. Getting better at managing stress can help. Even something as simple as deep breathing can lessen the effects of stress. Or try other relaxation techniques, such as:

  • Meditation
  • Yoga
  • Other types of exercise

Counseling can make a big difference, too.
 

It’s Got Agents Standing By

Other than your nervous system, your immune system is the most complex system in your body. It’s made up of tissues, cells, and organs, including:

  • Your tonsils
  • Your digestive system
  • Your bone marrow
  • Your skin
  • Your lymph nodes
  • Your spleen
  • Thin skin on the inside of your nose, throat, and genitals

All of these help create or store cells that work around the clock to keep your whole body healthy.

A fever can help your immune system fight infections in two ways. A higher temperature in the body speeds up how cells work, including the ones that fight illness. They can respond to invading germs faster. Also, higher body temperatures make it harder for bacteria and viruses to thrive in your body.

It Learns From Your Past

You’re born with a certain level of protection, or “immunity.” But it can get better.

Think of a baby or young child who comes down with colds, earaches, or other everyday illnesses often and babies who are breast feed continue to get antibodies from their mother while they are making their own.. Their immune system is creating a "bank" of antibodies as they are exposed to illnesses for the first time, enabling them to fight off future invaders. 

Vaccines work in much the same way. They turn on your immune system by introducing your body to a tiny amount of a virus (usually a killed or weakened one). Your body makes antibodies in response that protects against threats like measles, whooping cough, flu, or meningitis. Then, when you come in contact with that virus in your everyday life, your immune system is already primed to kick in so that you don’t get sick.

It Can Change Over Time

Your immune system can become less effective as you get older. That can make you more likely to get sick or get infections. You are also more susceptible to infections as you age or if you have a weakened immune system. And those infections, especially flu and pneumonia, are more likely to be fatal than in younger people.

Why it happens isn't clear. It may be about your immune system slowing down. Or it could be partly linked to nutrition, since seniors often eat less and don't always get the nutrients they need to keep their immune systems strong. So eat lots of fruits and vegetables. They're good for you at any age.

Medical Conditions That Weaken Your Immune System

You might have heard that a flu vaccine weakens your immune system, but that’s not true. The vaccine prepares your immune system for the flu.

A flu vaccine teaches your immune system to recognize that virus as a threat. Some people may still get the flu after having a flu shot, but they'll probably have a milder form of the illness. That's because antibodies made in response to the vaccine can still provide some protection.

Some people may mistake the occasional short-lived side effects of the vaccine (slight fever, aches) for flu symptoms. And the time of year people are most likely to get the vaccine is when colds and other respiratory illnesses are common. If you get the vaccine and then get sick with an unrelated bug, you may assume, incorrectly, that the vaccine caused the illness.

On the other hand, conditions and medications that can weaken your immune system include:

  • Autoimmune diseases
  • Cancer
  • Steroids
  • Chemotherapy

Seasonal allergies can be caused by an abnormal response

Allergy symptoms happen when your immune system reacts to something harmless, like pollen, pet dander, or mold. Your body sees the allergen as an invader and attacks it, giving you a runny nose and itchy eyes.

People can inherit a tendency toward allergies; if you have allergies, your children have a higher chance of having them, although they may be allergic to different things.

Allergies are treated by avoiding your allergy triggers and taking medication to control symptoms. For some people, allergy shots may be an option. Over a period of time, usually several years, allergy shots may help your immune system get used to the allergen, so that it doesn't produce the bothersome allergy symptoms.

You Can Help It Out

The classic things that keep your heart, brain, bones, and the rest of you well are also good for your immune system:

  • Stay active.
  • Work to keep your weight healthy.
  • Don’t smoke.
  • If you drink alcohol, keep it moderate (no more than one drink a day if you’re a woman, and two drinks daily if you’re a man).
  • Eat nutritious foods.

While no single food will upgrade your immune system, poor nutrition can have a negative effect on the immune system. What counts is having a balanced diet.

Just about everyone could stand to eat more fruits and vegetables. They're rich in vitamins and minerals that are good for you. If you’re thinking about getting supplements to cover your nutritional needs, check with your doctor or a dietitian. Chances are, you’re getting what you need from food, unless you're on a strict diet, are pregnant, or have certain medical conditions.

WebMD Medical Reference

Sources

SOURCES:

American College of Rheumatology: "The immune system and its link to rheumatic disease."

CDC: "Immunity types," "Vaccines and immunizations" and "Alcohol and public health." 

Harvard Medical School: "How to boost your immune system."

National Institute of Allergy and Infectious Diseases: "Immune System."

University of Rochester Medical Center: "All about the immune system."

U.S. National Library of Medicine: "How does the immune system work?" and "What are the organs of the immune system?"

Vaccines.gov: "Immunity: Natural and acquired."

Glasser, R. Nature Reviews: Immunology, March 2005.

WebMD Feature: "Top 12 Flu Myths."

WebMD Medical Reference in Collaboration with Cleveland Clinic: "Allergy Shots."

WebMD Health News: "Cautious Optimism Over Cancer Vaccine."

Brigham and Women's Hospital: "Drinking Tea May Boost Immune System."

FamilyDoctor.org: "When Your Infant or Child Has a Fever."

The Cleveland Clinic: "Diet, Exercise, Stress and the Immune System."

Harvard Health Report: "The Truth About Your Immune System."

Rowe, C. Journal of the American College of Nutrition, October 2007.

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