28596
In about 75 % of cases , the underlying causes remain unknown , and the term chronic idiopathic urticaria ( CIU ) is used to emphasize that wheals develop independently of identified external stimuli .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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