A flare, in medical terms, is a temporary worsening of symptoms in someone who has a chronic disease that was previously stable or in remission. The word shows up across rheumatology, gastroenterology, dermatology, pulmonology, neurology, and oncology, always pointing to the same basic idea: the disease is asserting itself again. In rheumatoid arthritis, one of the most studied contexts, an international working group formally defined a flare as “worsening of signs and symptoms of sufficient intensity and duration to lead to change in therapy.”1PubMed. Developing a construct to evaluate flares in rheumatoid arthritis: a conceptual report of the OMERACT RA Flare Definition Working Group That definition captures the spirit across conditions, but the details of what counts, what triggers it, and how you manage it vary enormously depending on the disease.
How Flares Differ From Relapses, Exacerbations, and Attacks
Medical language can be confusing because different specialties use different words for what sounds like the same thing. In multiple sclerosis, a relapse is defined as a sudden clinical episode with symptoms typical of MS, developing over hours to days, lasting more than 24 hours, and occurring without fever or infection.2Book of Abstracts – RAD 2025 Conference. A relapse of multiple sclerosis classifiable as an acute clinical event with stable magnetic resonance imaging (ACES) In asthma, doctors often say “exacerbation” or “acute episode.” In gout, the preferred term is “flare” or sometimes “attack.” These words are not perfectly interchangeable. A relapse in MS implies new neurological damage, while a gout flare implies an inflammatory explosion in a joint that may resolve completely. But all of them describe the same basic pattern: a condition that seemed controlled suddenly isn’t.
The practical distinction that matters most is between a flare and disease progression. In cancer treatment, for example, imaging that shows apparent worsening can sometimes reflect a “flare phenomenon” rather than the tumor actually growing. Distinguishing the two is critical because a flare may resolve on its own, while true disease progression requires a change in treatment. Misdiagnosing one for the other can lead to unnecessary delays or unnecessary treatment changes.3PubMed Central. Flare response versus disease progression in patients with non-small cell lung cancer
What Happens in the Body During a Flare
The underlying biology depends on the disease, but a common thread runs through most flares: an overactivation of the immune system. In autoimmune diseases and many inflammatory conditions, the immune system attacks the body’s own tissues or overreacts to a trigger. During stable periods, medications or the body’s own regulatory mechanisms keep this activity in check. A flare means that control has broken down.
In gout, the mechanism is particularly well understood. Uric acid crystals that have been sitting in joint tissue get recognized by immune cells called macrophages. Those cells activate an internal alarm system known as the NLRP3 inflammasome, which leads to the release of inflammatory signaling molecules, triggering the intense pain, redness, and swelling of a gout attack.4PubMed Central. Lower Temperatures Exacerbate NLRP3 Inflammasome Activation by Promoting Monosodium Urate Crystallization, Causing Gout The original discovery that uric acid crystals activate this pathway helped explain why gout behaves the way it does, flaring violently and then calming down, rather than producing constant low-grade symptoms.5PubMed. Gout-associated uric acid crystals activate the NALP3 inflammasome
In lupus, rheumatoid arthritis, and inflammatory bowel disease, the mechanisms are messier. Multiple immune pathways can be involved simultaneously, and the trigger for any given flare is often unclear. What’s clear is that the inflammatory cascade amplifies itself: immune cells release signaling molecules that recruit more immune cells, which release more signals, creating a feedback loop. In extreme cases, this kind of runaway inflammation is sometimes described as a cytokine storm, where the immune response itself becomes more dangerous than the original trigger.6PubMed Central. The ‘cytokine storm’: molecular mechanisms and therapeutic prospects Most disease flares don’t reach that level of severity, but the principle of inflammatory self-amplification is the same.
Common Triggers
If you live with a chronic inflammatory disease, you’ve probably noticed that flares don’t arrive randomly. Certain triggers are well recognized across conditions.
Stress is one of the most consistent. In psoriasis, mental stress was found to be strongly associated with exacerbation, with people reporting stress having roughly five times the odds of a psoriasis flare compared with an eczema flare. Inadequate sleep also showed a significant association with psoriasis worsening.7PubMed Central. Factors Associated with Exacerbation in Psoriasis Compared to Eczema The stress connection shows up in lupus, IBD, and rheumatoid arthritis too, though the strength of the link varies.
Infections are another classic trigger. The COVID-19 pandemic provided a vivid example: the virus itself, along with the emotional stress of the pandemic, was documented to trigger psoriasis flares in people with the condition.8International Journal of Advanced Engineering Research and Science. Flare up phenomenon in psoriasis after SARS-CoV-2 infection Severe COVID-19 infections can unleash a flood of inflammatory signaling molecules, and elevated levels of these molecules were consistently found in patients with severe disease.9PubMed. The roles of critical pro-inflammatory cytokines in the drive of cytokine storm during SARS-CoV-2 infection For people with pre-existing inflammatory diseases, that systemic immune activation can tip a smoldering condition into full flare.
Other well-known triggers include medication changes (especially stopping or reducing treatment too quickly), hormonal shifts during pregnancy or menstruation, environmental factors like weather or allergens, and dietary factors in conditions like gout and IBD. The environmental picture can be surprisingly specific: eczema exacerbations, for instance, are more strongly linked to humidity and dust exposure than psoriasis flares are.7PubMed Central. Factors Associated with Exacerbation in Psoriasis Compared to Eczema
Why Gout Flares Hit at Night
People with gout often notice that their worst attacks strike in the middle of the night or early morning. This isn’t coincidence. Research has found that uric acid crystals alter the internal clocks of immune cells, disrupting the normal circadian cycle that keeps inflammation suppressed during sleep. In laboratory macrophages, exposure to uric acid crystals reduced the levels of clock proteins that normally hold the NLRP3 inflammasome in check, leading to time-of-day differences in how easily the inflammasome could be activated.10PubMed. Monosodium urate crystals alter the circadian clock in macrophages leading to loss of NLRP3 inflammasome repression: Implications for timing of the gout flare Lower temperatures in peripheral joints during the night may also promote crystal formation, compounding the problem.4PubMed Central. Lower Temperatures Exacerbate NLRP3 Inflammasome Activation by Promoting Monosodium Urate Crystallization, Causing Gout So if you’ve ever wondered why your toe wakes you up at 2 a.m., it’s your immune cells losing their internal brakes at exactly the wrong time.
How Flares Are Diagnosed and Measured
Diagnosing a flare sounds like it should be straightforward: the patient feels worse. But in practice it’s complicated. Many chronic diseases exist on a spectrum, and deciding whether someone’s symptoms represent a true flare, a bad day, or something unrelated (like an infection that mimics flare symptoms) requires clinical judgment.
In lupus, diagnosis is primarily clinical, meaning doctors rely on the pattern of symptoms after ruling out infections and other causes. Blood tests measuring complement levels and anti-DNA antibodies can help track disease activity, but they lack high diagnostic accuracy on their own.11PubMed Central. Flares in systemic lupus erythematosus: diagnosis, risk factors and preventive strategies In pediatric lupus, distinguishing a flare from an acute infection is especially tricky. Researchers have found that combining several blood markers, including the ratio of certain white blood cell types, hemoglobin levels, and complement levels, can predict flare status with good accuracy.12PubMed Central. Differential parameters between activity flare and acute infection in pediatric patients with systemic lupus erythematosus The challenge is that no single number reliably separates “flare” from “not flare” in most diseases.
In rheumatoid arthritis, researchers developed a questionnaire called the FLARE-RA, which scores symptoms from 0 to 10. The cutoffs for clinical significance vary with disease duration: for patients with RA lasting two to five years, a score of 2 suggests a flare is present, while a score of 5 suggests treatment should change. For patients with RA for more than five years, the treatment-change threshold drops to 3.5, reflecting the reality that longer-standing disease may need earlier intervention.13PubMed. Definition and construct validation of clinically relevant cutoffs on the Flare Assessment in Rheumatoid Arthritis (FLARE-RA) questionnaire
When Patients and Doctors Disagree
One underappreciated aspect of flares is that patients and their physicians don’t always agree on whether one is happening. In a study of early rheumatoid arthritis patients, patients and doctors agreed on flare status only about 72% of the time. When patients said they were in a flare, they tended to report more tender and swollen joints than their doctors counted, with the difference averaging nearly four joints for tenderness and more than two for swelling.14ACR Meeting Abstracts. Patient Self-Assessments and Selected Patient-Reported Outcomes May Reliably Identify Rheumatoid Disease Flare in Early Rheumatoid Arthritis Patients
This gap isn’t because patients are exaggerating. Pain, fatigue, and functional limitation are real experiences that don’t always show up on the physical exam or in lab results. In inflammatory bowel disease, a large proportion of patients who appear to be in clinical remission actually have ongoing mucosal inflammation that hasn’t caused noticeable symptoms yet.15PubMed. Majority of patients with inflammatory bowel disease in clinical remission have mucosal inflammation This means the relationship between inflammation and symptoms is not always straightforward. You can have inflammation without symptoms, and you can feel awful when the labs look relatively normal. Both situations create diagnostic confusion around flares.
Predicting Flares Before They Arrive
One of the most frustrating aspects of living with a flare-prone condition is the unpredictability. You feel fine, you make plans, and then symptoms slam back. Research is increasingly focused on catching flares before they fully develop.
In IBD, a stool marker called S100A12, which is produced by inflammatory white blood cells, showed promise as an early warning system. In patients who were in remission, levels of this marker began climbing up to six months before a clinical relapse. At a specific cutoff, the marker could predict relapse eight to twelve weeks in advance with a sensitivity of about 70% and specificity of about 83%.16PubMed. Improving relapse prediction in inflammatory bowel disease by neutrophil-derived S100A12 That’s not perfect, but it’s far better than waiting for symptoms to appear.
Wearable devices represent a newer frontier. A study of rheumatoid arthritis patients found that physiological data from wearable sensors, including metrics like heart rate variability and skin temperature, could detect changes up to 28 days before both inflammatory and symptomatic flares. The models achieved remarkably high accuracy, with sensitivity and specificity both above 95% for predicting inflammatory flares in that window.17PubMed Central. Wearable devices detect physiological changes that precede and are associated with symptomatic and inflammatory rheumatoid arthritis flares These results are early and will need confirmation in larger, real-world settings, but they suggest a future where your smartwatch might warn you that a flare is brewing before you feel the first twinge.
How Flares Are Treated
Treatment depends on the disease, the severity, and what the patient is already taking, but a few principles are broadly consistent.
Corticosteroids are the workhorses of acute flare management across many conditions. In asthma exacerbations, a review of the evidence found that systemic corticosteroids speed recovery and reduce the risk of relapse. Oral and intravenous forms appear similarly effective, and a course of five to ten days without tapering is sufficient for most patients who are sent home from the emergency department.18PubMed Central. An umbrella review: corticosteroid therapy for adults with acute asthma In severe lupus flares, high-dose intravenous corticosteroid pulses are sometimes used over several days, often combined with other immune-suppressing therapies.
For diseases like Crohn’s disease and ulcerative colitis, biologic medications, particularly those targeting a protein called tumor necrosis factor, are widely used to both induce remission and prevent future flares. These are often combined with traditional immune-modifying drugs like thiopurines.19PubMed Central. Biologic monotherapy versus combination therapy with immunomodulators in the induction and maintenance of remission of Crohn’s disease and ulcerative colitis The goal with these long-term medications isn’t to treat the flare after it arrives but to keep the immune system in check so flares happen less often. When they do break through, short-term escalation of steroids or a switch in biologics is common.
A key treatment principle that applies broadly: don’t reduce or stop your medications because you feel good. Feeling well often means the treatment is working, not that you no longer need it. Many flares are triggered by exactly this kind of well-intentioned dose reduction.
The Financial Weight of Flares
Flares aren’t just a medical problem. They hit patients financially through direct healthcare costs, lost work, and reduced quality of life. In systemic lupus erythematosus, the average cost of a single flare in the United States was roughly $2,600 for patients without kidney involvement and about $5,800 for those with lupus nephritis. Severe flares were dramatically more expensive, averaging close to $15,000 per episode without kidney involvement and about $29,000 with it.20PubMed Central. The cost of flares among patients with systemic lupus erythematosus with and without lupus nephritis in the United States
In generalized pustular psoriasis, a rare but severe skin condition, patients who experienced flares had nearly twice the hospitalization rate of those who did not. Pharmacy and total charges climbed steeply with repeated flares, reaching averages above $50,000 for patients with two or more episodes.21PubMed Central. GPP Flares Linked to Increased Hospitalizations, Health Care Costs, Study Finds These figures underscore why preventing flares, not just treating them, is such a priority in chronic disease management. Every flare avoided is a hospitalization that doesn’t happen and a bill that doesn’t arrive.
Silent Inflammation and the Flare That Hasn’t Happened Yet
Perhaps the most unsettling finding in flare research is that the absence of symptoms doesn’t always mean the absence of disease activity. In inflammatory bowel disease, a majority of patients who were clinically in remission, meaning they felt fine and had no obvious symptoms, still had detectable mucosal inflammation on endoscopy.15PubMed. Majority of patients with inflammatory bowel disease in clinical remission have mucosal inflammation About a third of those patients saw their inflammation resolve spontaneously, but the rest had ongoing subclinical disease that was essentially waiting in the wings.
This concept of subclinical or smoldering inflammation exists across diseases. In rheumatoid arthritis, imaging studies sometimes reveal joint inflammation that hasn’t yet produced pain. In lupus, serological markers can be abnormal months before symptoms return. The practical implication for patients is that routine monitoring matters even when you feel well. Relying purely on how you feel can mean missing the opportunity to intervene before a full flare develops, especially in diseases where cumulative damage from repeated flares leads to irreversible problems like joint destruction, kidney scarring, or bowel strictures. That’s the real argument for staying on medications and keeping your monitoring appointments: the flare you prevent is always cheaper and less harmful than the one you treat after it arrives.