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Background Atopic dermatitis (AD) is often associated with allergic asthma (AA). Inhalation of allergens influences the activity of AA but the effect on the skin in AD is unclear. Objectives We evaluated the degree of bronchial hyperresponsiveness to methacholine in eight AD patients with AA (AD+) and eight AD patients without AA (AD-) and studied bronchial and cutaneous responses after allergen inhalation challenge. Methods All patients were treated in hospital for their eczema with tar ointment (pix liquids) and orally administered antihistamines (mean hospital stay 37 days). After clearing of the skin lesions allergen inhalation challenge was performed. Cutaneous responses were studied by measuring the 'Costa' score before and 24 h after allergen inhalation challenge. Results The median value of the provocative concentration of methacholine causing a 20% fall (PC20 Mch) in forced expiratory volume in 1 second (FEV1) was significantly higher in the AD- group compared to the AD+ group with median values of 10.70 and 0.60 mg/mL, respectively. These values did not change significantly in both groups during hospital stay. After challenge all AD+ patients showed early and late asthmatic responses whereas only four AD- patients showed early asthmatic responses (mean values of the maximal fall in FEV1 during the EAR 37%/16% and in PEF during the LAR 27%/4% for AD+ and AD- patients, respectively). The 'Costa' score increased in both groups (mean score before 19.1/24.4 and after challenge 26.8/26.9 for AD+ and AD- patients, respectively). The increase in the AD+ group was significantly higher compared with the AD- group (P = 0.016). Conclusion We conclude that allergen inhalation challenge causes a flare up of the skin lesions in atopic dermatitis patients. This was more prominent in atopic dermatitis patients who already suffered from an IgE-mediated allergic inflammation in the lung. [ABSTRACT FROM AUTHOR]