A 98-year-old woman presented with a 4-month history of an eczematous dermatitis that started on both ears and spread to the temples and forehead (Fig 1). She had been prescribed topical steroid preparations, which provided some relief. She wore in-the-ear hearing aids for her presbycusis. Patch-tested with 46 standard allergens as well as her steroid creams, the patient showed a single reaction to epoxy resin (1% weight per weight in petrolatum). We accessed Web postings on hearing aids and found epoxy resin to be used in some devices. Communication with the manufacturer of the patient's hearing aids revealed bisphenol A to be a monomeric component of the epoxy resins in her devices.
Eczematous dermatitis of an ear with an inserted hearing aid.
Epoxy resins are an increasing cause of occupational contact dermatitis.[1,2] Because of their excellent adhesiveness, high physical strength, and easy curing, they are also used in a wide variety of commercial products (such as adhesives in clothing and elastics, coatings for technological devices and electrical wiring, roofing and flooring materials, and adhesives).[1,2] Approximately 75 to 90% of epoxy resins are based on diglycidyl ether of bisphenol A, formed by combining epichlorohydrin and bisphenol A.[2–4] An epoxy resin offers little use in itself; the addition of a hardening agent polymerizes the epoxy resin, resulting in final "curing" of the product.
In-the-ear hearing aids are manufactured in several parts. Resting in the external auditory meatus, the hearing aid's hollow shell houses all of the electronics of the device. A plastic faceplate that displays all of the control elements of the device must be bonded to the shell. At this point in manufacturing, the epoxy resin is cured by the addition of hardening agents. Heat or exposure to ultraviolet light often facilitates this curing process. However, if the process is incomplete and any uncured resin remains, the sensitizing monomeric constituents can leak from the device onto the skin.
Epoxy resins and hardeners can individually cause irritation or sensitization and have been shown to cause allergic contact dermatitis. Due to their greater ability to penetrate the skin, low-molecular-weight epoxy resins are more sensitizing than higher-molecular-weight resins. Resins with molecular weights of 340 and 624 have higher allergenic potential. Amine hardeners, in particular, are powerful irritants and sensitizers that are generally encountered in the occupational setting. Fortunately, completely cured epoxy resin is relatively nonsensitizing and nonirritating.[3,4] Allergic contact dermatitis can be due to exposure to other substances in hearing aids, including methyl methacrylate and various other plastics. Other ear dermatitides that should be excluded are seborrheic dermatitis and contact dermatitis from nickel and other metals in jewelry.
After a consultation with the patient's audiologist, the device was sent back to the manufacturer for re-curing to reduce the amount of bisphenol A that could potentially leak from it. This intervention resulted in the resolution of the eruption, even after reuse of the cured hearing aids.
This case highlights the potential for epoxy resin in adhesives to cause allergic contact dermatitis from the use of hearing aids.
Dermatitis. 2011;22(06):350-351. © 2011 American Contact Dermatitis Society