The CPT is conducted using standardized and registered allergen extracts (ALK- Abelló, Hørsholm, Denmark). At the first visit, a titrated quantitative CPT (tqCPT) is performed according to a standardized protocol. In case of a positive test result, CPT-results are to be confirmed at a re-challenge one week later. The final CPT takes place 3 to 4 weeks after the 2nd (confirmatory) challenge for analyzing the primary objective of the trial: reproducibility of the CPT symptom score. Furthermore, objective evaluation of the clinical reactions after the tqCPT is documented using a MATLAB software program to calculate the degree of redness in percent. This is then correlated with the (subjective) main investigators' evaluations and with the external observer's evaluations.