Determination of the Sensitivity and Specificity of Prick Test Betula Verrucosa

General inclusion criteria for both groups: * Positive skin prick test with the positive control (Histamine HCl at 10 mg/mL). The length of the largest diameter of the wheal induced by this control should be ≥ 3 mm. * Negative skin prick test with the negative control. The length of the largest diameter of the wheal induced by this control should be \< 3 mm. * All ages and both genders. For the group of patients CH+ (true positive to Betula verrucosa): All these patients had a previous diagnosis of allergy to the birch pollen: * A positive case history with inhalant allergy related to exposure to birch pollen. * A positive skin prick test (mean wheal diameter ≥ 3 mm) when tested with a biologically standardized extract prepared from birch pollen. This preparation, from another manufacturer, was the one used in the routine in the Hospital. * Positive test for specific IgE (CAP value \> 0.35 IU/mL). For the group of patients CH- (true negative to Betula verrucosa): All these patients had a previous diagnosis of allergy to agents unrelated to birch pollen. * A negative case history with inhalant allergy related to exposure to birch pollen or to pollen with known cross-reactivity with the birch pollen. These patients could be allergic to other pollen or other allergens, such mites. * A negative prick test (largest diameter of the wheal ≥ 3 mm) when tested with a standardized extract prepared from the allergen source in question. * A negative test for specific IgE (CAP value \< 0.35 IU/mL) to birch pollen or to pollen with known cross-reactivity with birch pollen: Corylus avellana, Quercus verrucosa, Fagus sylvatica, Castanea satavia, Carpinus betelus and Alnus glutinosa. Exclusion criteria for both groups: * Patients that were using drugs that may interfere with the skin prick tests. * Patients using the following drugs 24 hours before the test: theophylline, systemic corticosteroids. * Patients in which the largest diameter of the wheal induced by the positive control was \< 3 mm. * Patients in which the largest diameter of the wheal induced by the negative control was ≥ 3 mm. * Pregnancy, dermographism, atopic dermatitis (locally at the test site), urticaria. * Patients who suffer disease in which the use of adrenaline is not allowed. * Patients with any severe psychiatric disease. For the patients CH+: • Patients that received or are treated with immunotherapy with an allergenic extract of birch pollen and/or with allergen extracts with known cross-reactivity to birch pollen (Corylus avellana, Quercus verrucosa, Fagus sylvatica, Castanea satavia, Carpinus betelus and Alnus glutinosa). For the patients CH-: * Patients sensitized to pollen with demonstrated cross-reactivity with the pollen of Betula verrucosa. These pollen included Corylus avellana, Quercus verrucosa, Fagus sylvatica, Castanea satavia, Carpinus betelus and Alnus glutinosa.