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What is a compromised immune system & what causes it?

When your immune system is working properly, you don’t even notice it, but when you have a compromised immune system, or your immune system becomes under- or over- active, you're at a greater risk of developing infections and other health conditions.

Compromised immune system 

When your immune system doesn't work properly, it's called an immune system disorder. These include: 

  • Primary immune deficiency: When you're born with a compromised immune system

  • Acquired immune deficiency: When you get a disease that causes a compromised immune system

  • An allergic reaction: When your immune system is too active

  • Autoimmune disease: When your immune system turns against you

Immune system disorders

Underactive immune system & immunodeficiency disorders

An immunodeficiency disorder is where your body cannot generate the right immune responses against invading microorganisms. An underactive immune system doesn't function correctly and makes people vulnerable to infections. It can be life threatening in severe cases. Some common examples include:

  • Severe combined immunodeficiency (SCID): This is an immune deficiency that is present at birth, where children are missing important white blood cells and are in constant danger of infections from bacteria, viruses, and fungi. 

  • Temporary acquired immune deficiencies: A compromised immune system can be caused by certain medicines, such as chemotherapy or other drugs used to treat cancer. It can also happen to people who have had organ transplants and take medicine to prevent organ rejection. Infections like the flu virus, mono (mononucleosis), and measles can also weaken the immune system for a brief time. Additionally, your immune system can be weakened by smoking, alcohol, stress, poor sleep and poor nutrition.

  • AIDS: HIV, which causes AIDS, is an acquired viral infection that destroys important white blood cells and weakens the immune system. People with HIV/AIDS become seriously ill with infections that most people can fight off. These infections are called “opportunistic infections” because they take advantage of weak immune systems. 

Overactive immune system 

If you are born with certain genes, your immune system may react to substances in the environment that are normally harmless. These substances are called allergens. Having an allergic reaction is the most common example of an overactive immune system. Dust, mould, pollen, and foods are common allergens. Overactivity of the immune system can take many forms, including: 

  • Allergies and asthma: Allergies are an immune-mediated inflammatory response to normally harmless environmental substances known as allergens. The body overreacts to an allergen, causing an immune reaction and allergy symptoms such as coughing, sneezing, runny nose or itchy rash. This can result in one or more allergic diseases such as asthma, allergic rhinitis, atopic dermatitis and food allergies.

  • Autoimmune diseases: Autoimmune diseases cause your immune system to attack your own body’s cells and tissues in response to an unknown trigger. The cause of autoimmune diseases is unknown, although it is thought to be a combination of a person’s genes and something in the environment that triggers those genes. Examples of autoimmune diseases include rheumatoid arthritis, lupus, inflammatory bowel disease, multiple sclerosis and type 1 diabetes.

What can weaken the immune system?

In addition to immune system disorders mentioned above, additional factors can contribute to a compromised immune system.

  1. Insufficient sleep: Lack of sleep, or not getting enough good quality sleep, can make you more prone to catching viruses or germs. This is mainly because your body releases certain proteins, called cytokines, that help the immune system defend against illness only during sleep. 

  2.  Low vitamin D: Vitamin D plays a key role in the immune system. It works to modulate both the innate and adaptive immune responses which are equally important in fighting infections.

  3. Poor diet: A diet low in fruits and vegetables and high in processed and refined carbohydrates and sugar can upset the balance of bacteria in the gut, lower your body’s ability to make healthy white blood cells and lead to low levels, or potential deficiencies, in zinc, vitamins A, C and E as well as antioxidants and polyphenols.

  4.  Smoking: Many of the chemicals found in cigarette smoke can cause a compromised immune system by changing the balance of immune cell production and function, therefore causing it to work less effectively. It can also reduce the levels of antioxidants in the bloodstream, including vitamin C levels.

  5.  Alcohol: Over consuming alcohol can cause a compromised immune system, making you more vulnerable to infections caused by bacteria and viruses. 

  6.  Lack of exercise: Physical activity acts as a modulator of the immune system. During and after physical exercise, pro- and anti-inflammatory cytokines are released and circulation increases which helps blood get around your body more efficiently so germ-fighting substances can get to where they need to go. 


Your immune system is a complex interactive system which works together to protect the body from viruses, bacteria and any foreign substances that can make you unwell. When it is working properly, you don’t even notice it. But when the performance of the immune system is compromised, that’s when you are likely to face illness. Luckily, there are steps that we can take to help make sure our immune systems are functioning properly. Find out more here.




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