Allergic Contact Dermatitis: Early Recognition and Diagnosis of Important Allergens

Sharon E. Jacob; Tace Steele


Dermatology Nursing. 2006;18(5):443-439, plus 4. 

In This Article

Antimicrobial Preservatives and Antimicrobials

There is a consumer tendency to seek out a product's active ingredients when purchasing a new product, while deeming the inactive ingredients to be superfluous information. Often, these inactive ingredients contain known sensitizing antimicrobial preservatives. The preservatives are ubiquitous in medical creams and ointments, lotions, make-up, and shampoos, for example, as they are added to extend the shelf-life of these products. Companies are permitted to change the ingredients of their products, without completely redesigning the label. While the ingredient list may change, many persons do not realize that a similar label could contain alternate ingredients. This necessitates careful instruction on label reading. Although many product labels do not list inactive ingredients, companies are still under disclosure mandates. One exception to this is products not regulated by the U.S. Food and Drug Administration (FDA), such as herbal remedies. Allergies to these can be seen in patients with chronic skin diseases, who subsequently use these medications or in more sensitive infrequent users. Two of the most common antimicrobial allergens are notoriously seen in several over-the-counter products, namely first aid kits. A common misconception is that over-the-counter is synonymous with benign or inert, but with each medication there is an inherent risk and benefit ratio that should be evaluated since many contain potential allergens.

Neomycin is a topical antibiotic found in the ointments used daily for minor cuts and abrasions (Neosporin, polysporin) and in medicated eye and ear drops. In fact, people who have had frequent otitis externa are more likely to have a sensitivity reaction to neomycin (Van Ginkel, Bruintjes, & Huizing, 1995). These patients can then develop systemic dermatitis if treated with an aminoglycoside antibiotic, such as gentamicin, which stimulates the immune system through cross reactivity.

Bacitracin, an antibiotic, is added to medications and eye drops similarly to neomycin. Actually, it is often combined with neomycin and other antibiotics in first aid products. Due to the increasing exposure to this antibiotic ointment, bacitracin has landed near the top of the list for common allergens in the United States. There have been reports that 2% of patients who use bacitracin postoperatively have a reaction but, more importantly, there have also been several reports of anaphylaxis (Gette, Marks, & Maloney, 1992; Jacob & James, 2004).

Thimerosal, an organic mercurial compound, is used as a preservative in vaccinations (tetanus) and cosmetics. Like many other preservatives, it is found in a wide variety of otic and ophthalmic solutions, including contact lens solutions and cleansers. Patients with thimerosal allergies can have an acute hypersensitivity reaction to vaccinations. The Public Health Agency in Canada has recommended that these patients receive their vaccinations in an environment with resuscitation capabilities (Canada Communicable Disease Report, 2003). Additionally, the FDA has put forth the discontinuation or minimalization of use in U.S. vaccines (FDA, 2005).

Methylchloroisothiazolinone/Methylisothiazolinone (MCI/MI) is a preservative that is commonly used in cosmetics, shampoo, and bubble bath, but also has a utility as a pesticide. The last decade has seen a replacement of solvent-based paints with more ecologically friendly paints such as water-based paints. These new paints need more preservatives than their predecessors, and MCI has quickly taken its place as the most common preservative in water-based paints (Reinhard et al., 2001). This has led to more and more patients presenting with an airborne contact dermatitis from the MCI in the paint. These patients present with a rash on their air-exposed skin and respiratory symptoms (Bohn, Niederer, Brehm, & Bircher, 2000).

Parabens are some of the most widely used preservatives found in consumables (mayonnaise, frozen dairy products, jellies) to leave-on products (eye shadow, sunscreen, lotions). Parabens are found in rectal and vaginal creams, as well as injectable and topical anesthetics. Notably, while parabens are the most prevalent preservative in all topical therapeutic preparations, they are the least sensitizing overall. In the allergic individual however, the allergic response can be smoldering, dramatic, and systemic (, 2005a). This underscores the importance for patients with an allergy to inform all of their health care providers to assure avoidance.

An allergy to formaldehyde-releasing preservatives and formaldehyde is very common due to its widespread use. Of course, this goes hand-in-hand with the difficulty of avoidance. For example, cigarettes are preserved with a formaldehyde resin, so patients are at risk for exposure by smoking or second-hand smoke (Schaller, Triebig, & Beyer, 1989). The current guideline is for formaldehyde content to be less than 0.2% for leave-on products; however, 5% is permissible in nail polish as a hardener (International Programme on Chemical Safety, 2002). Cosmetics, home cleaners, baby wipes, deodorants, and shampoos are important sources for exposure. Wrinkle-free clothing is treated with a formaldehyde textile resin, and dry cleaning is a process using formaldehyde (Rietschel & Fowler, 1995). Patients with allergies to formaldehyde commonly present with trouser dermatitis, which is a dermatitis between the thighs or behind the knees due to friction between clothes and skin (, 2005b).


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