Mast cell heterogeneity in chronic idiopathic urticaria. Patients with chronic urticaria are more sensitive to codeine skin testing than other allergic individuals. Nonlesional skin in most patients with chronic urticaria was found to contain increased numbers of both total and atypical mast cells. The presence of increased mast cell density was found to correlate with the degree of clinical (dermatographism) and functional (codeine skin test) skin sensitivity. 