Yes, prednisone lowers your immune system. It belongs to a class of drugs called glucocorticoids, and suppressing immune activity is both one of its intended effects and one of its most important side effects. How much it suppresses your immunity depends on the dose you’re taking and how long you’ve been on it.
How Prednisone Suppresses Immunity
Prednisone works by dialing down several layers of your immune defense at once. It blocks the production of key signaling molecules that your immune cells use to coordinate their response to threats. These include proteins responsible for triggering inflammation and rallying other immune cells to fight off infections. Without these signals, your body’s alarm system is effectively muted.
It also changes how immune cells move through your body. Normally, white blood cells travel through your bloodstream to wherever an infection or injury is occurring. Prednisone interferes with that process by reducing the sticky molecules on blood vessel walls that help immune cells exit the bloodstream and reach infected tissue. The result is a temporary drop in the number of lymphocytes (the immune cells responsible for targeting specific threats like viruses and bacteria) circulating in your blood. Your neutrophil count, a different type of white blood cell, actually rises on prednisone, which can make a standard blood test look misleadingly normal or even elevated. This is a well-documented lab quirk: the total white blood cell count goes up while the cells that matter most for fighting infections go down.
Dose and Duration Matter
Not every prednisone prescription carries the same level of immune risk. Doses of 40 mg per day or higher are considered “high dose” and carry the most significant immunosuppressive effects. At lower doses, the picture is more nuanced. In randomized controlled trials, short courses at lower doses have generally shown little to no measurable increase in infection risk. One pooled analysis found that infection rates were nearly identical between people on short, lower-dose steroid courses (5.8%) and those not taking steroids at all (5.4%).
However, observational studies that follow people in real-world settings tell a different story for longer use. Even doses as low as 5 mg per day have been associated with a small but real increase in the risk of serious bacterial infections when taken for a week or more. That risk climbs in a stepwise fashion the longer you stay on the drug: the same 5 mg daily dose roughly doubled the odds of serious bacterial infection when taken continuously for three years compared to a single week.
So a five-day burst of prednisone for a bad asthma flare is a very different situation from taking 20 mg daily for six months to manage an autoimmune condition. Both suppress your immune system to some degree, but the practical infection risk scales with how much you take and for how long.
Which Infections Become More Likely
Prednisone doesn’t raise the risk of every infection equally. A large population study comparing people prescribed glucocorticoids to unexposed individuals found the biggest increase in risk was for lower respiratory tract infections, including pneumonia, where the risk was nearly six times higher. Skin infections like cellulitis roughly doubled. The risk of sepsis, a potentially life-threatening bloodstream infection, was also elevated.
On the viral side, prednisone is particularly associated with reactivation of dormant viruses already living in your body. Shingles (caused by the chickenpox virus reactivating) is a well-documented risk. Hepatitis B reactivation is another concern for people who carry that virus. Notably, the study found no increased risk of new chickenpox infection, common fungal skin infections, or scabies.
For fungal infections, local candidiasis (oral or vaginal yeast infections) was more common in people on glucocorticoids. The risk of these infections, along with lower respiratory infections, was highest during the first weeks of use and decreased over time as the body adjusted.
Effects on Vaccine Response
Because prednisone suppresses immune activity, it can blunt your body’s ability to build protection from vaccines. If you’re taking less than 7 mg per day, your vaccine responses are generally maintained. Above 20 mg per day, antibody levels and the likelihood of developing full protection drop measurably. The middle range of 7 to 20 mg daily is less clear, with studies showing inconsistent results.
Non-live vaccines (like flu shots, COVID vaccines, and tetanus boosters) are safe to receive while on prednisone, even if they may be somewhat less effective. Live vaccines, such as the shingles vaccine or the MMR vaccine, are a different concern. In people with significantly suppressed immune systems, live vaccines can potentially cause the very infection they’re designed to prevent. If you know you’ll be starting a longer course of prednisone, getting vaccinated beforehand is ideal when timing allows.
How Long Immunity Stays Suppressed After Stopping
Your immune system doesn’t bounce back the moment you stop taking prednisone. When you’ve been on it for more than a couple of weeks, your adrenal glands, which normally produce your body’s own version of this hormone, have been suppressed. They need time to wake back up and resume normal production. This is why doctors taper the dose gradually rather than stopping abruptly.
Full recovery of immune function takes anywhere from about a week to several months, depending on how high your dose was and how long you were taking it. A short burst of a few days requires little to no tapering and immune recovery is quick. Someone coming off months of high-dose therapy may need a slow taper over weeks, and their immune system may remain somewhat suppressed throughout that period.
Practical Steps While You’re On It
The most important precaution while taking prednisone is avoiding exposure to infections when you can. That means staying away from people who are visibly sick, washing your hands frequently, and being especially cautious around anyone with chickenpox or measles, both of which can be severe in immunosuppressed people. Prednisone can also mask the early symptoms of an infection, so a fever or sore throat you’d normally shrug off might represent something more significant while you’re on this medication.
If you’re on a longer course, pay attention to respiratory symptoms. Given the sharply elevated risk of lower respiratory infections, a cough that lingers or worsens is worth having evaluated sooner rather than later. The same goes for skin wounds that become red, warm, or swollen, since cellulitis risk is also increased. Oral thrush, a white coating on the tongue or inner cheeks, is a common and treatable sign of yeast overgrowth that can appear within the first few weeks of use.