What Causes a Weakened Immune System?

You’ve probably heard a lot about how important your immune system is, especially over the past few years. Phrases like “herd immunity” and “immunocompromised” proliferated in official public health updates, news stories, and health care centers as experts navigated all the uncertainties of the COVID-19 pandemic. Now, we know that the virus can affect anyone, but it can lead to particularly risky complications for the most vulnerable people in our communities.¹

Of course, the immune system’s job is to protect your body from all invaders that may be harmful, not just certain viruses: When functioning properly, it alerts your body to a wide range of potential threats and helps it respond accordingly. However, some people have dysfunctional immune systems—which are also known as weakened or compromised immune systems—that cause their bodies’ protective response to be under- or overactive, per Johns Hopkins Medicine.

There’s no exact figure for how many people live with weakened immune systems, but it’s safe to say it’s in the millions, Leonard Calabrese, DO, a rheumatologic and immunologic disease expert at the Cleveland Clinic, tells SELF. Some research suggests at least 7 million adults in the United States are immunocompromised, per the Centers for Disease Control and Prevention (CDC). 

Below, experts explain the factors that can break down the immune system’s defenses, the common symptoms associated with compromised immune systems, and what kinds of treatments are available to help.

What is a weakened immune system, exactly?

Your immune system is an intricate network of cells, tissues, and organs (as well as the substances they make) that, generally speaking, fight disease and infection, according to the National Institutes of Health (NIH). White blood cells may come to mind, but there are lots of body parts that play important roles in your immune health, like your skin, lymph nodes and vessels, thymus gland (which makes white blood vessels), spleen, tonsils, and bone marrow, among others.

The immune system is generally broken down into two parts, Scott Weisenberg, MD, an infectious disease specialist at NYU Langone Health, tells SELF. These are called the innate (or inherited) and the adaptive (or acquired) immune systems. The major difference between the two is that you’re born with the former, and your body develops the latter.² 

The innate immune system is the first to respond to an invader—such as a harmful germ—by surrounding it with protective cells and, if all goes as planned, killing it. The adaptive immune system supports your innate response by producing proteins called antibodies.² These are designed to counter a specific threat, like certain viruses or bacteria, should your body be exposed to them and need backup in the future, per Johns Hopkins Medicine.

Problems can occur when the immune system either doesn’t respond enough or responds too strongly, Dr. Calabrese says. “A compromised immune system fails to either detect danger or [reacts] aggressively and causes collateral damage to our systems,” he explains.³

It’s worth noting that problems with the immune system exist on a spectrum, Dr. Calabrese adds. The potential health risks posed by a weakened immune system aren’t the same if you’re comparing one person who, for example, has moderate allergies, to someone who’d recently had an organ transplant. “They’re hardly in the same category,” Dr. Calabrese says.

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What causes a weakened immune system?

Any number of health issues, such as mild asthma, can affect your body’s ability to fight disease and infection—and certain lifestyle factors, like smoking tobacco and not getting enough sleep, can also interfere with your body’s ability to stay balanced and heal, the CDC says. However, there are several major factors that can compromise your immune system’s defenses. These include:

Autoimmune diseases

Autoimmune diseases are characterized by a malfunctioning immune response; essentially, your body goes a bit rogue and starts to attack its healthy cells, tissues, and organs, according to the National Institutes of Health (NIH). There are more than 80 autoimmune diseases that experts know of, including rheumatoid arthritis, type 1 diabetes, lupus, and many more; these conditions are thought to impact at least 24 million people in the United States, while an additional 8 million are estimated to have blood markers that point to their susceptibility of developing one of these disorders, per the NIH.