Contact Dermatitis in Auto Mechanic? Think Isothiazolinones

HERSHEY, PA. — A new onset of dermatitis in an auto mechanic should raise clinical suspicion for contact allergy to isothiazolinone preservatives found in many car repair and maintenance products, Bruce A. Brod, M.D., said at a meeting on contact dermatitis sponsored by Pennsylvania State University.

In an illustrative case of allergic contact dermatitis to isothiazolinones, Dr. Brod described a nonatopic male auto mechanic who owned a diesel fuel station and auto repair shop. The man presented with a 5-month history of a “horrific, nearly erythrodermic” dermatitis involving his hands, arms, legs, and trunk. While he responded very well to systemic steroids, the dermatitis would completely clear when he was away from work for weeklong vacations.

Besides patch testing with the North American Contact Dermatitis Group standard series, Dr. Brod also used an oil and cooling fluid series, a plastic and glue series, a rubber additive series, and a corticosteroid series. The most relevant positive results on patch testing included the isothiazolinones 5-chloro-2-methyl-4-iso- thiazolin-3-one (MCI), 2-methyl-4-isothiazolin-3-one (MI), and 2-n-octyl-4-isothiazolin-3-one (OIT), said Dr. Brod of the department of dermatology at the University of Pennsylvania, Philadelphia.

He began a search for isothiazolinones in the patient's environment. “It's quite an undertaking in somebody who works around a lot of [industrial] products in an auto shop.” After searching for isothiazolinones in the patient's personal care products, such as his moisturizers, cleansers, and topical medications, Dr. Brod read through material data safety sheets for the industrial chemicals and products in the auto shop and called companies to learn about the chemicals in motor oils and other automotive fluids.

“As a last resort and just an afterthought, we asked him if he worked with any sort of adhesives because there have been some reports of octyl-isothiazolinone present in some adhesives,” Dr. Brod said.

The man reported working with a silicone gasket sealant. Material data safety sheets did not identify OIT in the sealant, but the toxicologist working for the sealant's manufacturer confirmed its presence.

Although the mechanic's widespread dermatitis improved when he avoided the sealant, he still had the condition on his hands and forearms at a 2-month follow-up visit. The man admitted to pumping diesel fuel for customers at the fuel station since his duties at work had become limited because of his avoidance of numerous auto parts and products. A toxicologist working for the oil company confirmed that some of the businesses that refine oil for the company (which does not have its own oil refinery) added OIT and MCI to their storage tanks.

The patient's dermatitis cleared almost completely when be began avoiding the diesel fuel. Isothiazolinones are added to diesel fuel because diesel's high water content makes it vulnerable to microbial overgrowth. A bus mechanic in the Netherlands also has been reported to react to MCI/MI in diesel fuel (Contact Derm. 1996;34:64–5).

Besides silicone sealants, the fungicide OIT (also known under the trade names Kathon 893 and Skane M-8) is found in products such as wallpaper adhesives, water-based paints, cutting oils, and leather preservatives. Allergic contact dermatitis to OIT has been reported in painters, paint factory workers, and laboratory workers. No nonoccupational cases have been published, because OIT is “not really used in the personal care industry,” Dr. Brod said.

The North American Contact Dermatitis Group's 2001–2002 study of patch testing of 65 allergens on 4,913 patients showed that 2.3% of patients had positive reactions to MCI and MI. Of the patients with positive reactions, 88% had a current or past episode of dermatitis from exposure to MCI and MI.