Because of their anti-inflammatory activity, corticosteroids generally mask the clinical signs of a contact dermatitis to a corticosteroid preparation. The lesions usually present as chronic dermatitis, and the patients mostly report not exacerbations but failures to respond to corticosteroid therapy, Moreover, masking also occurs with patch-test reactions obtained with corticosteroid preparations and the corticosteroid molecules themselves. These are important reasons why contact allergy to such preparations has frequently been missed in the past.