||Contact dermatitis is a localized, delayed Type IV (cellmediated) hypersensitivity reaction. The Langerhans,cells are the antigen-processing and antigen-presenting cells, while sensitized lymphocytes (T cells) are the reacting cells. Tissue damage results from various lymphokines released by the T cells.
Since sensitization, once established, is present on every part of the patient's skin, patch testing of a sensitized person is often of value in identifying the causative substance.
Contact dermatitis of the external ear is relatively common, and is frequently confused with infectious otitis externa. One important differentiating feature is that patients with contact dermatitis complain primarily of itching rather than pain.
This hearing aid user developed itching, scaling, and erythema in the conchal bowl, in an area corresponding to the position of his plastic ear mold. The contact dermatitis was treated with topical cortisone ointment, and a new hypoallergenic ear mold made.