Most often, only a small part of the immune system is weak, which makes infections from specific, not all, bugs more likely. Some people have stronger immune systems than others, so they are resistant to more types of infections.

A few people, very few, are resistant to all types of infections. Unfortunately, most people find out that one part of their immune system is weak when they get an infection.

But there is no single test that checks out the immune system. Age plays a big role in the immune system. Young children, exposed to infections for the first time, tend to be symptomatic more than adults.

And older adults may find their immune system cannot fight disease as well as it did when they were young. Scientists are studying direct connections between lifestyle choices and strong immune systems. What we know now is that healthy living is good for overall health and vaccinations are the best supplement available.

Most studies show that dietary supplements are only useful if you have a deficiency in a nutrient. Taking supplements on top of a healthy diet does not add much to your immune system.

Note that most supplements are not superior to the nutrients you can get from food. Studies show the immune system is very responsive to exercise. Exercise and immune regulation are interrelated and affect each other. The scientist can only measure things that may reflect stress, such as the number of times the heart beats each minute, but such measures also may reflect other factors.

Most scientists studying the relationship of stress and immune function, however, do not study a sudden, short-lived stressor; rather, they try to study more constant and frequent stressors known as chronic stress, such as that caused by relationships with family, friends, and co-workers, or sustained challenges to perform well at one's work.

Some scientists are investigating whether ongoing stress takes a toll on the immune system. But it is hard to perform what scientists call "controlled experiments" in human beings.

In a controlled experiment, the scientist can change one and only one factor, such as the amount of a particular chemical, and then measure the effect of that change on some other measurable phenomenon, such as the amount of antibodies produced by a particular type of immune system cell when it is exposed to the chemical.

In a living animal, and especially in a human being, that kind of control is just not possible, since there are so many other things happening to the animal or person at the time that measurements are being taken.

Despite these inevitable difficulties in measuring the relationship of stress to immunity, scientists are making progress.

Almost every mother has said it: "Wear a jacket or you'll catch a cold! Probably not, exposure to moderate cold temperatures doesn't increase your susceptibility to infection. There are two reasons why winter is "cold and flu season. Also the influenza virus stays airborne longer when air is cold and less humid.

But researchers remain interested in this question in different populations. Some experiments with mice suggest that cold exposure might reduce the ability to cope with infection.

But what about humans? Scientists have performed experiments in which volunteers were briefly dunked in cold water or spent short periods of time naked in subfreezing temperatures.

They've studied people who lived in Antarctica and those on expeditions in the Canadian Rockies. The results have been mixed. For example, researchers documented an increase in upper respiratory infections in competitive cross-country skiers who exercise vigorously in the cold, but whether these infections are due to the cold or other factors — such as the intense exercise or the dryness of the air — is not known.

A group of Canadian researchers that has reviewed hundreds of medical studies on the subject and conducted some of its own research concludes that there's no need to worry about moderate cold exposure — it has no detrimental effect on the human immune system. Should you bundle up when it's cold outside?

The answer is "yes" if you're uncomfortable, or if you're going to be outdoors for an extended period where such problems as frostbite and hypothermia are a risk. But don't worry about immunity. Regular exercise is one of the pillars of healthy living. It improves cardiovascular health, lowers blood pressure, helps control body weight, and protects against a variety of diseases.

But does it help to boost your immune system naturally and keep it healthy? Just like a healthy diet, exercise can contribute to general good health and therefore to a healthy immune system. As a service to our readers, Harvard Health Publishing provides access to our library of archived content.

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What can you do to boost your immune system? Photos courtesy of Michael N. There are plenty of resources on HIIT exercise — for all different fitness levels and body types. Importantly though, it is good to remember not to overdo it with your exercise.

Excessive exercise can temporarily reduce the immune system function. Research has shown that up to 90 minutes of intensive exercise can increase your cortisol and adrenalin levels for 72 hours, reducing immune function. Researchers believe that the human gut is home to at least trillion microbial cells — an order of magnitude greater than the number of human cells on your body!

In fact, you could say that there are approximately 10 times more microbial cells in the human body than human cells, and the collective gut microbial genome is at least times larger than the human genome. Research from the early s has focused on the relationship between human and microbial cells.

It is now understood that there was a symbiotic relationship in our evolution and that the gut microbes we carry with us evolved with us along the way. Well, the human gut and the immune system work together to promote a healthy body.

The gut microbiome releases immunity cells called helper T-cells, which assist antibodies with tracking and destroying pathogens and toxins in our bodies. The immune system also communicates with the gut microbiome by assisting the growth of symbiotic microbes.

In return, the gut microbiome helps to develop enzymes required for a healthy immune response. While natural options and lifestyle changes are typically the go-to advice for immune system stress support, these are not always sufficient to completely prevent getting an infection.

Some pathogens are too strong for our immune system and can wreak havoc in our bodies, no matter how healthy we are. Vaccines are biological preparations designed to produce an acquired immunity to a pathogen — usually a virus.

Around the world, we have eradicated one major disease — smallpox — and all but eradicated polio. In the United States, several diseases have almost been eradicated, including measles, bacterial influenza, measles, mumps, rubella, and tetanus. In fact, the World Health Organization lists 25 vaccines that are proven to be effective against human diseases.

Nevertheless, there has recently been a counter-movement against vaccines, fuelled by a number of different beliefs, ranging from fear of allergies to elaborate conspiracy theories. It is important to remember that vaccines save millions of lives each year — approximately 3 million — and a further 1.

For most people, getting enough sleep, exercising regularly, eating healthily, staying immunised, and supporting a healthy gut microbiome is more than enough to promote a healthy immune system — even during times of stress. However, if you have an immune disorder — for example, a compromised immune system or an overactive immune system, you may need to get medical treatments for extra support in stressful times.

Examples of diseases that compromise the immune system, reducing its ability to work and leaving the patient susceptible to infections, include:.

Treatments for these diseases depends on the underlying condition. Typically, drugs like antibiotics, antiviral and anti-fungal medications are given for each infection. Immunoglobulin therapy and antiretroviral drugs may also be used. In severe cases, bone marrow transplants might be ordered.

As we get older, our immune systems begin to lose some of their potency, increasing the risk of disease and cancer. This is why countries with higher life expectancies tend to have a greater incidence of age-related conditions. Research indicates that, compared to young people, older persons are more likely to contract infectious diseases, and are also more likely to die from them.

On an immune level, the body starts to reduce the production of helper T cells and B cells also known as primary lymphocytes as we age. This is thought to be due to changes in stem cells, local tissue, and systemic environments, and it results in an increased occurrence of immune system stress.

The leading causes of death of people over the age of 65 tend to be heart disease, cancer, strokes, and respiratory diseases. Around the world, researchers are working on potential therapies to combat the decline in immune function in the elderly.

One leading theory has to do with a form of malnutrition, especially in wealthy countries where life expectancy is high. This is micronutrient deficiency — in which a person becomes deficient in essential vitamins or trace minerals as a result of their diet.

Micronutrients act as cofactors for enzymes and are vital for a healthy, strong immune system. As older people tend to eat less varied diets, they may risk becoming deficient in certain micronutrients, which can negatively impact the immune system.

Today, on-going stress is recognized as a key risk factor for increasing the likelihood of developing a disease, due to its effect in dampening our immune systems.

It is essential for us to make healthy lifestyle changes in order to boost our immune systems as much as possible. Key strategies to reduce immune system stress include adequate sleep, regular exercise, immunization, and good nutrition.

Research has revealed that increasing intakes of specific nutrients including zinc, vitamin A, selenium, vitamin D, and glutamine, may significantly enhance immune function.

To increase levels of these nutrients consumed, a balanced diet rich in fruits and vegetables is recommended. In conjunction with a healthy diet, a daily multivitamin containing these micronutrients should also be considered, especially during times of increased stress.

Given the immune-enhancing effects of adequate sleep, regular exercise, and good nutrition, these factors should collectively be recognized as fundamental parts of our immune systems. Current Directions in Stress and Human Immune Function.

Current opinion in psychology , 5 , 13— Stress and hormones. Indian journal of endocrinology and metabolism , 15 1 , 18— Sick and tired: does sleep have a vital role in the immune system? Nature Reviews Immunology, 4 6 , — Sleep deprivation potentiates HPA axis stress reactivity in healthy adults.

Health Psychology, 33 11 , — and Vijay-Kumar, M. Mammalian gut immunity. Biomedical journal , 37 5 , — Diet and Immune Function. Nutrients , 11 8 , Perceived stress, unhealthy eating behaviours, and severe obesity in low-income women. Nutrition Journal , 14 , E ffect of fruit and vegetable consumption on immune function in older people: a randomized controlled trial.

The American Journal of Clinical Nutrition, 96 6 , — Zinc-Altered Immune function. The Journal of Nutrition, 5 , S—S. Glutamine: Metabolism and Immune Function, Supplementation and Clinical Translation.

If a vaccinated person is exposed to the actual virus, bacterium or toxin, they won't get sick because their body will recognise it and know how to attack it successfully. Vaccinations are available against many diseases, including measles and tetanus.

The immunisations you may need are decided by your health, age, lifestyle and occupation. Together, these factors are referred to as HALO, which is defined as:. View the HALO infographic External Link to find out more.

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Actions for this page Listen Print. Summary Read the full fact sheet. On this page. Immune system The immune system and microbial infection Parts of the immune system The body's other defences against microbes Fever is an immune system response Common disorders of the immune system Immunisation Where to get help.

Immune system The immune system is made up of a complex network of organs, cells and proteins that fight infection microbes. The immune system and microbial infection The immune system External Link keeps a record of every microbe it has ever defeated, in types of white blood cells B-lymphocytes and T-lymphocytes known as memory cells.

Parts of the immune system The main parts of the immune system are: white blood cells antibodies complement system lymphatic system spleen bone marrow thymus.

White blood cells White blood cells are the key players in your immune system. Antibodies Antibodies help the body to fight microbes or the toxins poisons they produce. Complement system The complement system is made up of proteins whose actions complement the work done by antibodies.

Lymphatic system The lymphatic system is a network of delicate tubes throughout the body. The main roles of the lymphatic system are to: manage the fluid levels in the body react to bacteria deal with cancer cells deal with cell products that otherwise would result in disease or disorders absorb some of the fats in our diet from the intestine.

The lymphatic system is made up of: lymph nodes also called lymph glands — which trap microbes lymph vessels — tubes that carry lymph, the colourless fluid that bathes your body's tissues and contains infection-fighting white blood cells white blood cells lymphocytes.

Spleen The spleen is a blood-filtering organ that removes microbes and destroys old or damaged red blood cells. Bone marrow Bone marrow is the spongy tissue found inside your bones. Thymus The thymus filters and monitors your blood content. The body's other defences against microbes As well as the immune system, the body has several other ways to defend itself against microbes, including: skin — a waterproof barrier that secretes oil with bacteria-killing properties lungs — mucous in the lungs phlegm traps foreign particles, and small hairs cilia wave the mucous upwards so it can be coughed out digestive tract — the mucous lining contains antibodies, and the acid in the stomach can kill most microbes other defences — body fluids like skin oil, saliva and tears contain anti-bacterial enzymes that help reduce the risk of infection.

The constant flushing of the urinary tract and the bowel also helps. Fever is an immune system response A rise in body temperature, or fever , can happen with some infections.

Common disorders of the immune system It is common for people to have an over- or underactive immune system. Overactivity of the immune system External Link can take many forms, including: allergic diseases — where the immune system makes an overly strong response to allergens.

Allergic diseases are very common. Get support to help you quit tobacco from UC Davis Health experts. Highly processed foods include chips, cookies, refined grains, and deli meats. When you eat these foods every day, you do not have as much room for foods that are more nutritious, such as fruits, vegetables, and fiber-rich grains.

Eating less of these essential nutrients can decrease the chances that your immune system will defend against illness or recover quickly from it. Learn 4 healthy eating tips to keep your immune system in top shape. Find healthy eating tips and recipes in our Good Food As Good Medicine blog.

Stress causes inflammation, which has a negative impact on your immune system. Try to do what you can to minimize stress. That could mean taking a few deep breaths when things start to feel heated or get outside and go for a walk.

Getting more exercise in general is good for our blood sugar levels, our stress, and our overall health. Check out our stress management class. While sleep often tends to be a low priority in our busy lives, it has a huge impact on our health and ability to fight viruses and disease.

Get tips for better sleep in an age of anxiety. Find out how much sleep you really need from the Sleep Foundation. Age plays a big role in the immune system. Young children, exposed to infections for the first time, tend to be symptomatic more than adults.

And older adults may find their immune system cannot fight disease as well as it did when they were young. Scientists are studying direct connections between lifestyle choices and strong immune systems.

What we know now is that healthy living is good for overall health and vaccinations are the best supplement available. Most studies show that dietary supplements are only useful if you have a deficiency in a nutrient.

Taking supplements on top of a healthy diet does not add much to your immune system. Note that most supplements are not superior to the nutrients you can get from food. Studies show the immune system is very responsive to exercise.

Exercise and immune regulation are interrelated and affect each other. Exercise changes immune regulation by affecting cells and has anti-inflammatory effects.

Sleep loss reduces natural killer cell activity, which increases the risk for cancer and viral infections; generates production of inflammatory cytokines, which increases the risk for cardiovascular and metabolic disorders; and reduces production of antibodies, which increases the risk for infections.

Stress of all sorts—psychological and physical—directly weakens parts of your immune system, increasing risk for infections or reactivation of viruses inside you. Shingles, a painful rash that arises from the reactivated chickenpox virus, often flares up when people are experiencing chronic stress.

Stress can also cause "patrols" in your immune system—certain cells that tell the immune system to wind down an attack—to fail.