This study aims to identify subpopulations of patients with cholinergic urticaria based on their sensitivity to infrared (IR) radiation exposure. Cholinergic urticaria is a chronic inducible urticaria triggered by increased body temperature. The study seeks to determine whether infrared exposure can induce symptoms in a subset of patients and whether these patients exhibit specific clinical or epidemiological characteristics.

Cholinergic urticaria is characterized by small pruritic papules triggered by exercise, emotions, hot environments, or hot food and beverages. The pathophysiology remains unclear, but one hypothesis is that a central temperature increase plays a key role. A pilot study conducted at university hospital center (CHU) of Montpellier found that infrared exposure triggered symptoms in some patients with cholinergic urticaria. The infrared source was the same as that commonly used in photobiological tests.

The objective of this study is to identify the proportion of patients who develop cholinergic urticaria when exposed to infrared light. the investigators then aim to determine whether these patients have specific clinical or epidemiological characteristics that would allow them to be classified as a distinct subgroup of cholinergic urticaria and to assess whether sensitivity to infrared light is a prognostic marker of disease severity. Furthermore, measuring the core temperature of all patients during infrared light exposure will help determine whether patients sensitive to infrared light experience a greater increase in core temperature during the IR test. This would support the hypothesis that an increase in core temperature is responsible for triggering cholinergic urticaria flare-ups in this subgroup.

A better understanding of this condition and the identification of different subgroups could ultimately, with additional studies, allow for a personalized approach to patient management based on the cholinergic urticaria subgroup and each subgroup's sensitivity to different treatments.

Inclusion criteria :

• Adults ≥ 18 years old
• Cholinergic urticaria diagnosed based on the diagnostic criteria published in 2016 (Magerl et al) : pruritic micropapules triggered by active or passive exposure to heat.
• Exercise test performed within the 6 months prior to inclusion.

Exclusion criteria :

• Patients on H1 antihistamines within 72 hours before infrared exposure test
• Patients on any other specific treatment for cholinergic urticaria within a period of 5 plasma half-lives before infrared exposure test
• Patients with exercise-induced anaphylaxis (diet-induced or not)
• Patients with severe forms of cholinergic urticaria: angioedema, respiratory manifestations or anaphylaxis
• Participants who have reached the maximum compensation amount for their participation in research studies.
• Lack of consent (adults, non-emancipated minors, individuals unable to express consent, research conducted in emergency situations, etc.).
• Not being affiliated with or a beneficiary of a French social security scheme.
• Protected adults (under guardianship, curatorship, or judicial protection).
• Individuals participating in another research study with an ongoing exclusion period.
• Subjects deprived of liberty (Art. L. 1121-6) (by judicial or administrative decision, or involuntary hospitalization).
• Pregnant or breastfeeding women.
• Subjects who cannot read and/or write.