8 Signs Your Immune System May Be Weak, According To Doctors

While supporting the immune system is important, it raises the question: How do we know if our immune system could be stronger in the first place?

Chronic diseases or autoimmune diseases are the most obvious risk factors for impaired immunity. But "there are definitely things lifestyle-wise that can set you up for infection," says Randy Horwitz, M.D., Ph.D., immunologist and medical director of the Arizona Center for Integrative Medicine. For the generally healthy population with no underlying medical conditions, these can include an unhealthy diet, a high-stress job or home environment, and poor sleep.

All of these factors, in turn, may lead to physical and even psychological manifestations (feeling chronically overwhelmed and exhausted) that could indicate your immune health is less than ideal. 

It's important to keep in mind that the signs and symptoms below are not specific to a weakened immune system—they could also be related to a number of other factors or health conditions. For example, you might get sick all the time because you have a kindergartner who's constantly bringing home nasty germs. Or you might have chronic diarrhea because you keep eating dairy and you're actually lactose intolerant. 

"For the general population, for people who do get sick more frequently with a cold, or flu, or even pneumonia, it usually means that there's some break down in the immune system," says Heather Moday, M.D., physician and integrative immunologist. 

According to the CDC1, it's considered normal for adults to get two to three colds per year; and most people recover in seven to 10 days. In healthy people, this is plenty of time for your body to develop antibodies and fight off the disease. But if it takes you longer to recover—or you keep getting colds, sinus infections, ear infections, or really any infection—your immune system is struggling to keep up. 

If you don't have good sleep hygiene and snag less than eight hours of quality shut-eye per night, you're missing out on some pretty big benefits—and you can pretty much guarantee your immune function isn't optimal. 

Melatonin, the hormone your body releases when it gets dark so you get sleepy, is actually a really important immune mediator, too. "It causes certain immune cells to release cytokines, which, in turn, activate immune cells to fight infections," says Moday. "So when we sleep, we often have more recruitment and activity of certain white blood cells like macrophages and neutrophils, and natural killer (NK) cells, which have antiviral and anti-cancer actions in the body."

Subpar sleep, on the other hand, can suppress the activity of these cells, and "we also see less vigorous antibody responses—we don't make antibodies as well," says Moday.

If your work demands are nuts and you feel perpetually stuck in fight-or-flight mode, chances are high that your chronic stress is messing with your immune system. As with poor sleep, chronic stress can reduce the recruitment and action of certain immune cells and prevent the body from mounting the optimal antibody response, says Moday.

In fact, one study found that students' immunity decreased during a stressful three-day exam period. They produced fewer NK cells and their infection-fighting T-cells were less responsive. 

Excessive stress also means excessive levels of the "stress hormone" cortisol are pumping through your system, which "can weaken the immune system by weakening the gut-immune barrier," says Moday. "It does that specifically by lowering an antibody called IgA, which lines all of our mucus layers through the digestive tract and acts as a first line of protection." When this happens, viruses are able to more readily invade through the lining of the intestinal tract.

Depression and grief are other examples of emotional stressors that can impair immune function. In fact, there's a whole field of immunology called psychoneuroimmunology, which examines the connection between the emotions and the immune system. 

"In a famous study2, [the researcher] went to people who had just lost their partners or spouses in the hospital and drew their blood, and he showed that extreme grief is linked to an acute drop in immune reactivity," says Horwitz. "So your B-cells and T-cells aren't as responsive in periods of extreme stress and grief."

Additionally, even mild depression among older people can suppress the immune system, and feelings of loneliness and isolation have been linked to weakened immunity in college students.

Chronic diarrhea could indicate a weakened immune system for a number of reasons. For one, your diarrhea could potentially be caused by an infection or a parasite—and if you just can't seem to shake it, that might be an indicator your body isn't mounting a strong enough immune response to kill it, says Moday.

Chronic diarrhea could also be caused by a dysbiotic, or imbalanced gut microbiome, in which certain bacteria proliferate when they shouldn't. This can promote inflammation, reduce the integrity of the gut lining—both of which impair immunity. Think about it: About 70% of the body's immune system tissue3 is found in the gut, so it makes sense that unhealthy imbalances here would have reverberating effects on overall immunity.

Chronic diarrhea—whatever the cause—can also prevent you from absorbing all the nutrients from your diet. For example, if you're not absorbing enough fat, that could, in turn, prevent you from optimally absorbing fat-soluble nutrients, including vitamin D, that play a key role in immune health.

"When you eat a high-carbohydrate diet, or consume refined processed carbs and sugar, you are putting your immune system at a disadvantage," says Ali Miller, R.D., L.D., CDE, registered dietitian and certified diabetes educator. 

Your weight is another thing to consider—particularly if you fall into the obese category and/or have a high body fat percentage. Adipocytes (or fat cells) are pro-inflammatory and drive insulin resistance, which weakens the immune response. 

The skin is often a window into what's going on in the body—including the immune system, which can regulate inflammation and affect the barrier function and microbiome of the skin.   

"Recent research7 has highlighted that the immune system influences the types of microorganisms that live on your skin and affect your risk for disease," says Keira Barr, M.D., holistic and board-certified dermatologist. "So when the immune system is weakened, it can show up on the skin as eczema; allergic reactions; poor wound healing; bacterial, fungal, and viral infections such as herpes—and, depending on how weak the immune system is, the area affected could be localized or widespread." 

Skin symptoms related to the immune system could be manifesting for a number of reasons. For example, a poor diet and stress, which can cause immunosuppression and make your skin more vulnerable to problems, says Barr. 

If your alcohol consumption has spiked lately, there are more than a few reasons to scale back. But as it relates to immunity, "even if you're not an alcoholic, alcohol actually directly weakens white blood cells," says Moday. "It also causes a lot of inflammation of the gut, which can distress that gut-immune barrier."