What Causes a Weak Immune System?

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

  • 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 frequent and unusual infections. 
  • If you think you have a weak immune system, see a healthcare provider.

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, some 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.

One of the most common immunodeficiency syndromes is Immunoglobulin (IgA) deficiency. But there are many—more than 200—and they may go undiagnosed.

Other 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)  
  • Multiple myeloma, a type of blood cancer
  • Common variable immunodeficiency
  • BENTA disease

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, Elliott explained that corticosteroids are supposed to inhibit the activity of white blood cells.

That said, the benefits of the medications may outweigh the risks. Make sure to discuss the pros and cons with your healthcare provider.

Symptoms of a Weak Immune System

Here are some signs you can look out for that indicate a weak immune system.

You are getting sick more and staying sicker longer. Different people take different amounts of time to recover from an illness. If you have an infection that's taking much longer to clear up than usual (for you), or you are always sick with something, you might have a weak immune system.

Unusual infections. These are infections most people don't get and are sometimes called opportunistic infections (OIs).There are several types of OIs, which are more common and more severe than in people with healthy immune systems. They can include bacterial infections like tuberculosis, parasitic infections like toxoplasmosis, and fungal infections.

Infections that won't clear up. If you get the same kind of infection over and over or have a condition that won't clear with antibiotics or requires IV antibiotics, you may have a weak immune system.

Digestive problems. Long-lasting digestive problems such as chronic diarrhea may indicate a weak immune system.

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 Yourself

For people with weak immune systems, prevention is critical.

Healthcare providers recommend that you mask up if you have a weak immune system and get vaccinated against COVID-19. And, try to avoid people sick with something they can spread.

Ensure your home environment is safe by wiping down and sanitizing often-touched surfaces. Protect yourself from opportunistic infections by thoroughly cooking your food and ensuring your water is clean and safe. Wash your hands often.

Keep current on all your recommended vaccinations, and ask your healthcare provider which ones they are. Some aren't safe for people who have primary immunodeficiency.

Practice healthy habits like getting the proper nutrition, exercising regularly, and reducing stress and anxiety. And, finally, get plenty of sleep.

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12 Sources
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.
  1. National Institute of Allergy and Infectious Diseases. Overview of the immune system.

  2. National Library of Medicine. Immune system and disorders.

  3. Rawla P, Killeen RB, Joseph N. IgA deficiency. In: StatPearls. StatPearls Publishing; 2022.

  4. National Institute of Allergy and Infectious Diseases. Types of primary immune deficiency diseases.

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

  6. Immune Deficiency Foundation. About primary immunodeficiencies.

  7. Centers for Disease Control and Prevention. Primary immunodeficiency (PI).

  8. MedLine Plus. HIV and infections.

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

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

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

  12. Centers for Disease Control and Prevention. Six tips to enhance immunity.

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