The purpose of this study is to compare urticaria lesions (size, kinetics) by thermography, volumetry and digital time lapse photography in CU patients treated with desloratadine 5 mg or desloratadine 20 mg. Hypothesis: Updosing of desloratadine (20mg) is more efficient in the treatment of urticarial lesions as compared to standard dosing (5 mg desloratadine).

Inclusion Criteria:

1. Outpatients with moderate to severe CU for more than 6 weeks. Urticaria symptoms must comprise wheal and itch.
2. Patients must exhibit spontaneous urticaria lesions in the randomization visit.
3. History of beneficial effects of antihistaminic treatment.
4. Age between 18 and 60 years.
5. Female patients must be using adequate contraceptive precautions (highly effective method), or they must be postmenopausal, surgically sterilised, or hysterectomised (for details please see protocol).
6. Female patients must be using adequate contraceptive precautions (contraceptive pill, depot, double barrier methods), or they must be postmenopausal, surgically sterilised, or hysterectomised.
7. Voluntarily signed written informed consent.

Exclusion Criteria:

1. The presence of permanent severe diseases, especially those affecting the immune system, except CU.
2. The presence of permanent gastrointestinal condition which may influence the oral therapy (chronic diarrhea diseases, congenital malformations or surgical mutilations of the gastrointestinal tract).
3. History or presence of epilepsy, significant neurological disorders, cerebrovascular attacks or ischemia.
4. History or presence of myocardial infarction or cardiac arrhythmia which requires drug therapy.
5. Evidence of severe renal dysfunction
6. Evidence of significant hepatic disease (liver enzymes twice the upper reference value).
7. The presence of galactose intolerance, lapp lactase deficiency or glucose galactose malabsorption.
8. History of adverse reactions including hypersensitivity to DL and Loratadine.
9. Intake of medicaments that could cause QT changes (drugs listed on www.qtdrugs.org).
10. Presence of active cancer which requires chemotherapy or radiation therapy.
11. Presence of acute urticaria / angioedema including laryngeal edema
12. History or presence of alcohol abuse or drug addiction.
13. Participation in any clinical trial within 4 weeks prior to enrolment.
14. Intake of oral corticosteroids or other immunosuppressive therapy within 14 days prior to the beginning of the study.
15. Use of depot corticosteroids or chronic systemic corticosteroids within 21 days before beginning of the study.
16. Pregnancy or breast-feeding.
17. Existing or planned placement in an institution after ruling according to § 40 passage 1 number 4 AMG (Arzneimittelgesetz).