Generalized pustular psoriasis (GPP) is a rare, severe inflammatory skin disease in which sterile (non-infectious) pustules suddenly erupt across large areas of the body, often accompanied by high fever, fatigue, and other systemic symptoms. It affects roughly 1.6 to 3 people per 100,000, making it far less common than the plaque psoriasis most people are familiar with. GPP can develop in someone who already has plaque psoriasis or appear on its own with no prior skin disease.
What GPP Looks and Feels Like
The hallmark of GPP is the rapid appearance of small, pus-filled bumps on red, inflamed skin. These pustules are sterile, meaning they contain white blood cells rather than bacteria. They typically start in skin folds like the groin and armpits, then spread across the trunk and limbs. When many pustules sit close together, they can merge into larger sheets sometimes called “lakes of pus.” As a flare progresses, the pustules dry out and form brownish crusts or thick scales that eventually peel away.
Beyond the skin, a flare often feels like being seriously ill. High fever (above 38°C or 100.4°F) occurs in anywhere from 24% to 96% of patients during a flare. Other common symptoms include chills, nausea, diarrhea, joint pain, and deep fatigue. The skin itself can be intensely painful, burning, and itchy. Some people also develop swelling in the legs, eye inflammation (uveitis), or arthritis during or between flares.
What Drives the Disease
GPP is rooted in a malfunction of the innate immune system, specifically a signaling pathway controlled by a group of inflammatory proteins in the IL-36 family. In healthy skin, these proteins trigger a brief inflammatory response when needed, then get switched off by a natural braking molecule. In GPP, that brake fails.
The most well-understood genetic cause involves mutations in a gene called IL36RN, which produces the braking molecule. When IL36RN is mutated, the brake doesn’t bind properly to its receptor, and IL-36 signaling spirals out of control. Skin cells called keratinocytes begin pumping out more IL-36, which in turn triggers a cascade of other inflammatory signals. Those signals attract massive numbers of neutrophils (a type of white blood cell) into the upper layers of the skin, forming the visible pustules. In studies of Chinese patients with GPP, IL36RN mutations were found in 75% of cases. In an international cohort, about 21% carried mutations on both copies of the gene.
This self-reinforcing loop is key to understanding why flares can escalate so quickly. Once activated, mature IL-36 proteins become over 500 times more biologically potent than their inactive form. They stimulate keratinocytes to produce even more IL-36, plus a range of other inflammatory molecules that amplify the cycle further.
Common Triggers for Flares
GPP flares can seem to come out of nowhere, but identifiable triggers are common. The most widely recognized include:
- Corticosteroid withdrawal: Abruptly stopping oral corticosteroids is one of the most frequent triggers. Even the use of potent topical steroids under bandages or wraps has been linked to flare onset.
- Infections: Bacterial and viral infections are commonly reported triggers, and in some patients, GPP first appears after an infection with no prior history of psoriasis.
- Pregnancy: A specific variant historically called “impetigo herpetiformis” can develop during pregnancy. It carries an increased risk of stillbirth and fetal complications.
- Medications and physiologic stress: Various drugs and periods of significant physical stress can also precipitate flares.
Some people with longstanding plaque psoriasis develop GPP after exposure to one of these triggers, while others experience it as a new condition entirely.
How GPP Is Diagnosed
There is no single blood test for GPP. Diagnosis relies on the clinical picture: primary, visible pustules on non-acral skin (not limited to the hands and feet) that are not confined within existing psoriasis plaques. The European consensus definition specifies that GPP can occur with or without systemic inflammation, with or without plaque psoriasis, and can follow a relapsing pattern (more than one episode) or a persistent course lasting longer than three months.
One important diagnostic challenge is distinguishing GPP from a drug reaction called acute generalized exanthematous pustulosis (AGEP), which can look almost identical. A history of psoriasis and the presence of scaling plaques point toward GPP, while mucosal involvement (sores in the mouth or on other mucous membranes) is unique to AGEP. Skin biopsies can help: certain microscopic features like eosinophilic spongiosis and specific patterns of skin-cell damage favor AGEP, while the presence of particular immune cells (CD161+ cells) in the deeper skin layers strongly favors GPP.
Serious Complications
GPP flares can be life-threatening. The systemic inflammation that accompanies severe flares can overwhelm multiple organ systems, leading to sepsis, heart failure, kidney failure, liver failure, or respiratory failure. Dangerously low blood pressure and severe drops in blood calcium levels are also possible. Hospitalization is typically required during severe flares so that these complications can be caught early.
Mortality rates have improved significantly over the decades. A 1971 study reported a GPP mortality rate of 32%, but modern estimates range from 2% to 7%. In-hospital mortality sits around 4.2%, though that number varies sharply depending on treatment. Patients treated with corticosteroids alone had an in-hospital mortality rate of 9.1%, compared to just 1.0% for those treated with biologic therapies. Even between flares, GPP carries long-term risk: patients with GPP have roughly 1.5 times the mortality risk of those with plaque psoriasis alone, and nearly four times the risk of the general population after adjusting for other health conditions.
Treatment During and Between Flares
For decades, GPP had no specifically approved treatment, and doctors relied on broad immunosuppressants like cyclosporine, methotrexate, and retinoids to control flares. These are now considered third-line options. The first therapy specifically approved for GPP targets the IL-36 pathway directly. Spesolimab, approved by the FDA in 2022, blocks the IL-36 receptor and is given as a single intravenous infusion during an acute flare. If symptoms persist after a week, a second infusion can be administered.
Current expert guidance recommends biologic therapies targeting IL-36 signaling as first-line treatment when available. This reflects a growing understanding that GPP is mechanistically distinct from plaque psoriasis, and treatments designed for plaque psoriasis don’t always translate well. The older systemic therapies remain important where biologics are not accessible, but the shift toward targeted treatment has meaningfully improved outcomes, as reflected in the lower mortality rates seen with biologic use.
Between flares, ongoing management focuses on preventing recurrence. GPP tends to follow a relapsing course, and the unpredictability of flares is one of the most difficult aspects of living with the disease. The severity and frequency of flares vary widely from person to person, even among family members who share the same genetic mutations.