For a study, it was determined that GPP was a rare, possibly fatal condition marked by periods of extensive sterile macroscopic pustules, with or without systemic inflammation and/or plaque psoriasis. There were several GPP subtypes, ranging from severe von Zumbusch GPP to lesser annular pustular psoriasis. Generalized pustular psoriasis primarily affected adults, with a female predominance, however, juvenile GPP occurred as well. Flares were a defining feature of GPP and can occur spontaneously or as a result of stimuli such as systemic corticosteroids withdrawal, infections, stress, pregnancy, and menstruation. 

The severity of flares varied greatly between people and within a single patient. Systemic symptoms, most notably fever, general malaise, and extracutaneous signs such as arthritis, uveitis, and neutrophilic cholangitis, were frequently associated with significant flares. Neutrophilia, increased C-reactive protein levels, hypocalcemia, and abnormal liver function tests were all common laboratory findings. GPP’s clinical history was quite diverse; it might be a relapsing illness with recurring flares and no pustulation between flares, or it could be a permanent condition with constant moderate pustulation interrupted by more severe flares. 

Patients might experience several flares every year or only one per several years. The majority of flares lasted 2–5 weeks and required hospitalization in around half of the cases. Sepsis and renal, hepatic, respiratory, and cardiac failure are all life-threatening consequences. The reported death rate ranged from 2% to 16%.