When doctors prescribe steroids during an illness, they’re prescribing corticosteroids, a class of drugs that dial down your body’s inflammatory response. These are not the muscle-building anabolic steroids associated with athletics. Corticosteroids like prednisone and dexamethasone are used because many illnesses cause harm not just through the infection itself, but through the inflammation your immune system generates while fighting it. Steroids step in to keep that inflammation from doing more damage than the illness would on its own.
How Steroids Work During Illness
When you get sick, your immune system activates a cascade of inflammatory signals. Proteins called transcription factors flip on hundreds of inflammatory genes, which produce the chemicals responsible for swelling, redness, mucus, fever, and tissue damage. In many illnesses, this response overshoots what’s needed and starts harming healthy tissue.
Corticosteroids essentially reverse that switch. They enter your cells and change the structure of your DNA’s packaging so that inflammatory genes get turned back off. They also block the activity of key signaling proteins that would otherwise keep amplifying the immune response. The result is a broad suppression of inflammation: less swelling in your airways, less fluid in your lungs, less immune-driven tissue damage throughout the body. This is why steroids are useful across such a wide range of illnesses. They don’t treat the underlying cause, but they control the collateral damage your own body inflicts.
Asthma and COPD Flare-Ups
Respiratory conditions are one of the most common reasons you’ll be prescribed steroids when sick. During an asthma attack or a COPD exacerbation, the airways become swollen and constricted, making it difficult to breathe. Inhaled steroids are a daily preventive tool for many people with these conditions, but when a flare-up hits, oral steroids are often needed to bring the inflammation under control quickly.
For a COPD exacerbation severe enough to send someone to the emergency room, international guidelines recommend a short course of oral prednisone, typically 30 to 40 mg daily for 5 to 14 days. The goal is to reduce airway swelling fast enough that breathing improves within a day or two, preventing the need for hospitalization or mechanical ventilation.
Croup in Children
If your child has croup, that distinctive barking cough caused by swelling around the vocal cords, there’s a good chance the doctor will prescribe a single oral dose of dexamethasone. It’s one of the most well-studied and effective treatments for croup. Improvement typically begins within 2 to 3 hours and lasts 24 to 48 hours, which is usually enough time for the viral infection to start resolving on its own. Because it’s a single dose, the risk of side effects is minimal.
Severe Pneumonia and COVID-19
Steroids became a household topic during the COVID-19 pandemic, when dexamethasone was shown to save lives in patients sick enough to need supplemental oxygen. The recommended protocol was 6 mg of dexamethasone daily for up to 10 days, and it became standard care worldwide for severe COVID-19 pneumonia. Interestingly, higher doses didn’t perform better. In one randomized trial, patients on high-flow oxygen who received the standard 6 mg dose had 100% survival at 28 days, compared to just 57% survival among those given a much higher dose.
This finding highlights a key principle: steroids work best at the right dose for the right patient. In milder COVID-19 cases where patients didn’t need oxygen, steroids offered no benefit and could potentially make things worse by suppressing the immune system during a time when it still needed to fight the virus. The same logic applies broadly. Steroids are reserved for illness severe enough that inflammation itself has become a threat.
Severe Allergic Reactions
After a serious allergic reaction or anaphylaxis, you may be given a course of oral steroids alongside the initial emergency treatment. Steroids don’t work fast enough to stop anaphylaxis in the moment (that’s what epinephrine does), but they serve a different purpose: preventing a delayed second wave of symptoms, called a biphasic reaction, that can occur hours after the initial episode seems to have resolved.
Sepsis and Critical Illness
In sepsis, where an infection triggers a dangerous whole-body inflammatory response, low-dose steroids play a supporting role. Critical care guidelines suggest corticosteroids for adults in septic shock, particularly when blood pressure remains dangerously low despite fluids and other medications. The steroids help stabilize blood pressure and temper the runaway immune response. High doses given over a short period are actually harmful in this setting, which is why guidelines specifically recommend against them.
Autoimmune Flare-Ups
Steroids are a cornerstone of managing acute flare-ups in autoimmune conditions like lupus, rheumatoid arthritis, and psoriasis. In these diseases, the immune system mistakenly attacks the body’s own tissue, and a flare can cause rapid damage to joints, skin, kidneys, or other organs. A short course of steroids can halt that damage, improve symptoms, and sometimes push the disease back into remission. They’re often used as “bridge therapy,” controlling the flare while slower-acting long-term medications take effect.
Common Side Effects of Short Courses
Even a brief course of oral steroids can cause noticeable side effects. The most common ones are trouble sleeping, mood swings (ranging from irritability to feeling unusually energized or anxious), and spikes in blood sugar. If you have diabetes, you’ll likely need to monitor your glucose more closely while taking steroids. Some people also experience increased appetite, facial flushing, or a jittery feeling. These effects typically fade within a few days of stopping the medication.
The severity of side effects scales with dose and duration. A single dose of dexamethasone for a child’s croup is unlikely to cause anything noticeable. A 10-day course of prednisone for a COPD flare-up will probably disrupt your sleep and mood to some degree. None of these short-term effects are dangerous for most people, but they can be unpleasant enough that it helps to know they’re coming.
Why You Shouldn’t Stop Steroids Abruptly
If you’ve been on steroids for less than three to four weeks, your doctor will generally let you stop without tapering. But if you’ve taken them longer than that, your body may have partially shut down its own production of cortisol, the natural hormone that steroids mimic. Stopping suddenly in that situation can leave you without enough cortisol to function, a condition called adrenal insufficiency that can cause fatigue, dizziness, nausea, and in severe cases, a medical emergency.
A gradual taper gives your adrenal glands time to wake back up and resume normal cortisol production. The risk of adrenal problems is highest once the dose drops below the equivalent of about 5 mg of prednisone daily, because that’s roughly what your body would produce on its own. If you get sick with another illness during a taper, that added stress on your body can increase the risk of an adrenal crisis, so it’s important to let your doctor know.