Chronic spontaneous urticaria (CSU) is an inflammatory disease characterized by the presence of itchy wheals, angioedema, or both, for at least 6 weeks (1). Classically, CSU lasts from 1 to 5 years, and even longer in at least 10% of severe cases (2). For many patients, CSU is a self-limiting disorder, with only a single episode occurring during the patient’s lifetime. However, between 13% and 20% of patients with CSU may develop more than one episode, with long periods free of symptoms and treatment (3, 4). These patients do not fit into the classical concept of “intermittent acute urticaria”, given that each episode of CSU must last for more than 6 weeks, being active during months or even years. Therefore, we can consider the concept of “recurrent” CSU (RCSU). There have been few studies of patients with RCSU, or of the phenotype of these patients (3, 5). No differences between sexes have been observed in these patients, but they show less concomitant inducible urticaria, and stress appears to be the most common trigger of RCSU (4, 5). Patients with RCSU have shorter episodes and fewer psychiatric disorders (5).

There is no validated definition of RCSU, in terms of how long a patient must be asymptomatic and without treatment to diagnose whether a relapse of the same episode of CSU, or a new episode, is occurring. Kim et al. (4) defined recurrence of CSU when a new episode appears at least 6 months after cessation of the effective therapy and no symptoms are present.

To define the phenotypic features and risk factors in patients with previous episodes of CSU compared with those who develop only one episode, a validated definition of RCSU would be useful. The clinical expertise of dermatologists and allergologists is obviously of interest in this respect. Therefore, a survey was conducted among the 35 active members of the “Catalan and Balearic Chronic Urticaria Network (XUrCB)”. They were questioned about the minimum time required to make a difference between a relapse and a new episode of CSU. A recurrent or new episode of CSU was considered after a period of 3, 6, 9 and 12 months without symptoms and no treatment by 29%, 37%, 3% and 31% of the specialists, respectively. The median time until the new or recurrent episode began was 6 months, as found in previous studies (4).The answers were controversial among the XURCB’s members because there was a variation of opinions

In conclusion, it is proposed that CSU should be considered as a disease that can have more than one active chronic episode during a patient’s lifetime, lasting for more than 6 weeks, with some episodes lasting for months or even years, separated by periods with no activity during which no treatment is required. This behaviour defines a phenotype of patients with CSU. An agreed definition is required to define the time needed to distinguish be-tween a relapse of CSU and appearance of a new episode, and therefore to validate a definition of RCSU. This knowledge will be helpful to phenotypically understand patients with CSU.

To all members of Catalan and Balearic Chronic Urticaria Network (XUrCB): Ignasi Figueras Nart, Montserrat Bonfill Ortí, Nuria Lamas Domenech, Isabel Bielsa Marsol, Tono Guilabert Vidal, Ana Giménez Arnau, Laia Curto Barredo, Alba Álvarez Abella, Mercedes García Font, Vicente Expósito Serrano, Natalia Fernández, Eshter Serra Baldrich, Jorge Spertino, Xavier García Navarro, Carme Díaz Sarrió, Joan Garcias Ladaria, Ignacio Torné, Marta Vilavella, Carola Baliu Piqué, Jose Manuel Mascaró Galy, Sara Gómez Armayones, Carolina Prat Torres, Verónica Sanmartin Novell, Ramon Lleonart Bellfill, Anna Sala Cunill, Agustin Sansosti, Moisés Labrador Horrillo, Lluís Marquès Amat, Joan Bartra Tomas, Nathalie Depreux Niño, Paula Ribó González, and Mar Guilarte Clavero.

Conflicts of interest: GM-N received lecture fees from Novartis. Educational activities for Leo Pharma, Novartis, Sanofi, Almirall, Avène, Abbvie, Meda and Laboratorio Reig Jofre. Medical Advisor for Sanofi. LC-B received lecture fees from Novartis, Sanofi and Uriach Pharma. Educational activities for Leo Pharma and Sanofi. Medical Advisor for Sanofi. IF-N received lecture fees from Novartis, Sanofi, Leo Pharma and FAES pharma. Educational activities for Leo Pharma, Novartis and Sanofi. VE-S received lecture fees from Novartis. Educational activities for Leo Pharma, Novartis, Sanofi and Laboratorio Reig Jofre. Medical Advisor for Sanofi. XG-N received lecture fees from Novartis, Galderma and Abbvie. Educational activities for Leo Pharma and Gebro Pharma. AGV is Medical Advisor for Almirall and Cellgene. Research grants from Leo Pharma and Pfizer. Lectures fees from Novartis, Sanofi, Leo Pharma, Abbvie and Almirall. AMG-A is Medical Advisor for Uriach Pharma, Genentech, Novartis, FAES, GSK, Sanofi Research Grants supported by Uriach Pharma, Novartis, Grants from Instituto Carlos III-FEDER Educational activities for Uriach Pharma, Novartis, Genentech, Menarini, Leo-Pharma, GSK, MSD, Almirall, Sanofi.