Chronic spontaneous urticaria (CSU) is an immune-mediated skin disorder characterized by pruritic wheals and/or angioedema. This study aims to evaluate the relationship between diet-derived antioxidant capacity and oxidative stress with CSU presence, disease activity, and response to omalizumab. Adults with active CSU and age/BMI-matched healthy controls will provide non-consecutive 3-day dietary records (two weekdays and one weekend day). Dietary antioxidant capacity will be calculated using ORAC metrics via BeBiS software. Oxidative stress biomarkers (total oxidant status, total antioxidant status, oxidative stress index, malondialdehyde, and advanced oxidation protein products) will be measured from venous blood samples. CSU disease activity will be assessed using UAS7 and UCT, along with an urticaria quality of life questionnaire. In CSU patients who receive omalizumab as clinically indicated, assessments will be repeated after 3 months to evaluate treatment response and associated changes in diet and oxidative stress markers.

This is an observational, case-control study including 58 adults (18-65 years) with active chronic spontaneous urticaria recruited from a dermatology outpatient clinic and 58 age- and BMI-matched healthy volunteers. Demographic/clinical data and comorbidities will be recorded. Dietary intake will be captured using three non-consecutive 24-hour food consumption records (two weekdays, one weekend day). Food portions will be estimated using a standardized food photo catalogue and analyzed with BeBiS 9.0 to compute macro/micronutrients, glycemic index/load, and dietary antioxidant capacity using ORAC. Venous blood will be used to measure total oxidant status (TOS/TOK), total antioxidant status (TAS/TAK), advanced oxidation protein products (AOPP), and malondialdehyde (MDA), and to calculate oxidative stress index (OSI). In CSU patients, disease activity will be evaluated using UAS7 and the Urticaria Control Test (UCT), as well as an urticaria quality of life questionnaire. CSU patients with a clinical indication for omalizumab will be re-evaluated after 3 months, repeating dietary records, biomarker measurements, and clinical scores to assess treatment response.

Inclusion Criteria:

• Age 18-65 years
• CSU group: diagnosis of chronic spontaneous urticaria, active CSU, and written informed consent
• Control group: healthy volunteers with similar characteristics (age/BMI-matched)

Exclusion Criteria:

• Additional dermatologic, metabolic, endocrinologic, systemic inflammatory disease; malignancy (diagnosis or suspicion)
• Use within last 3 months of anti-inflammatory drugs or drugs that may affect serum glucose/lipids
• Special diet/nutrition status; antioxidant supplement use
• Smoking or alcohol use
• Pregnant or breastfeeding

Adults with active CSU and age/BMI-matched healthy volunteers