Chronic urticaria is characterized by skin lesions that repeatedly flare up for more than six weeks, with occurrences at least twice per week, and is known as chronic urticaria. Patients with chronic urticaria generally exhibit mild systemic symptoms. The welts vary in number, frequently reoccur, and can last for months to years. In cases of chronic urticaria, when patients consume certain foods or come into contact with specific allergens, they may suddenly experience symptoms similar to those of acute urticaria; this is referred to as an acute outbreak of chronic urticaria. Patients often experience sudden skin itching, and quickly develop welts of varying sizes that are red, round, oval, or irregular in shape. These welts may be distributed individually or merge into patches. Sometimes the welts turn pale, other times they become erythematous, and gradually disappear. In severe cases, patients may experience palpitations, chest tightness, decreased blood pressure, anaphylactic shock, or gastrointestinal mucosal symptoms such as nausea, vomiting, abdominal pain, and diarrhea. If the larynx swells, it can lead to difficulty breathing or even asphyxiation.