What Causes a Weak Immune System?

The immune system sometimes overreacts or doesn't work as it should, increasing the risk of infections.

The immune system is your body's defense mechanism, protecting you against viruses, bacteria, and other microorganisms that cause disease.

For most healthy people, the immune system succeeds in doing just that. However, the immune system sometimes overreacts or doesn't work as it should. In those cases, people are more susceptible to illness than others.

So, what exactly does it mean to have a weak immune system, and what causes it? Here's what you should know about having a weak immune system, including how to keep yourself and your loved ones healthy.

What Causes a Weak Immune System?

White blood cells are immune cells circulating in your body via your bloodstream, looking for any issues. White blood cells mostly do their job, seeking out foreign invaders and protecting the body against them. 

However, many health conditions and medications can affect their function. For example, some conditions can make the white blood cells overly aggressive, leading to an outsized response to small threats. A team of healthcare providers may treat the condition with medications that weaken your immune system.

In contrast, your white blood cells may do little or nothing in response to a real threat, leading to far more, or more severe, infections.

Some conditions that can cause a weak immune system include:

  • Diabetes
  • Cancer
  • Human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS)
  • Pregnancy
  • Alcohol use disorder
  • Liver or kidney disease  
  • Organ or tissue transplant
  • Inherited autoimmune conditions like lupus or rheumatoid arthritis (RA)  

Certain drugs and therapies can also cause a weak immune system, such as:

  • Immunosuppressants  
  • Corticosteroids medications for health conditions like lupus, sarcoidosis, inflammatory bowel disease (IBD), arthritis, or asthma
  • Tumor necrosis factor (TNF) inhibitors

Some of those drugs are explicitly made to weaken the immune system. Tania Elliott, MD, a clinical instructor of medicine at NYU Langone, told Health. For instance, corticosteroids are supposed to "inhibit the activity of the white blood cells," added Dr. Elliot.

That said, the benefits of the medications will almost always outweigh the risks.

Weak Immune System Symptoms

See a healthcare provider for possible treatment and diagnosis if you show symptoms of a weak immune system, like:

  • Getting sick more often and staying sicker longer than normal
  • Unusual infections
  • Infection that won't clear up
  • Swollen liver, spleen, or lymph nodes
  • Symptoms of autoimmune diseases like lupus, RA, and IBD
  • Being stressed out a lot

Risk Factors

Certain factors can increase your risk of having a weak immune system, including:

  • Having an autoimmune disease
  • Having a family history or risk factors for an autoimmune disease
  • Taking medications known to suppress immune function
  • Being a transplant recipient
  • Using prescribed corticosteroids
  • Having chronic stress
  • Undergoing treatment for cancer

How To Protect People With Weak Immune Systems

First, consider those with weak immune systems all the time, not just during a pandemic like COVID-19. The flu is another virus that, similarly to SARS-CoV-2, which causes COVID-19, affects people with weak immune systems more than others.

If you or someone you know has a weak immune system, one of the best ways to stay healthy is to limit contact with sick people as much as possible. Staying home and social distancing, if you're ill, are key.

If you're sick, some ways to protect people with weak immune systems include:

  • Wearing a mask in public if you're sick and at home, if you live with someone with a weak immune system
  • Limiting physical interactions with people outside your household
  • Washing your hands often

For people with weak immune systems, the following steps may help you stay healthy:

  • Stick with your treatment plan.
  • Thoroughly cook food and make sure water is clean and safe.  
  • Don't stop medication or treatment without talking to a healthcare provider.
  • Keep often-touched surfaces in your home clean and sanitized.
  • Keep anxiety and stress under control.
  • Keep up healthy habits like proper nutrition and regular exercise.
  • Stay up-to-date on all recommended vaccinations.

A Quick Review

Many factors can cause a weak immune system, from health conditions to medical procedures to certain medications. If you have a weak immune system, you may get sick often and take a long time to get over it, or you may have lots of frequent and unusual infections. 

If you think you have a weak immune system, see a healthcare provider and practice safety tips to stay healthy.

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Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. National Library of Medicine. Immune system and disorders.

  3. Centers for Disease Control and Prevention. People at risk – people with weakened immune systems.

  4. Immune Deficiency Foundation. CVID community center.

  5. Immune Deficiency Foundation. About primary immunodeficiencies.

  6. Bae YS, Shin EC, Bae YS, et al. Editorial: Stress and immunityFront Immunol. 2019;10:245. doi:10.3389/fimmu.2019.00245

  7. Centers for Disease Control and Prevention. People who are immunocompromised.

  8. American Medical Association. What doctors wish immunocompromised patients knew during COVID-19.

  9. Centers for Disease Control and Prevention. Prevention & control - immunocompromised persons.

  10. Centers for Disease Control and Prevention. General information for people with weakened immune systems.

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