Thimerosal Is The Fifth Most Common Allergen

Thimerosal, or sodium ethylmercurithiosalicylate, is a bacteria-killing preservative and antiseptic used in low concentrations in vaccines.

It has also been used in cosmetics, fluorescent dyes, ophthalmic and otolaryngologic medications, antitoxins, topical and intramuscular steroid preparations, and intradermal tests.

Introduced in the 1930s, its usage has largely been discontinued in recent years because of the mercury content and associated irritations. There are two components which are involved in thimerosal allergy: an organic mercury compound and thiosalicylate.

Common But Relatively Mild Allergen

According to the North American Contact Dermatitis Group (NACDG), thimerosal is the fifth-most common allergen. While many people are allergic, the reaction is quite mild. The NACDG states that it is one of the least relevant of the 65 allergens they test. Most patients are women with a type of dermatitis around the eyes resulting from cosmetic or contact lens solution containing thimerosal. Thimerosal has rarely been associated with systemic reactions like eczema. There has been only one case of obstructed airways reported which could be traced to a throat spray using thimerosal.


The effect of thimerosal on an adult with an allergy is swelling, redness and blisters, itching, burning and localized discomfort in the area of injection or contact, often the throat or eyes. If you experience these symptoms, a doctor would likely use the Thin-Layer Rapid Use Epicutaneous (TRUE) test to see if you are allergic to the preservative. This is a skin patch test. A positive result would yield a red swelling or irritation in the area of the patch. These symptoms can be treated with oral and topical antihistamines which can relieve itching and swelling resulting from exposure.


There are alternate vaccines which can be used for adults with a thimerosal allergy. There are also alternate choices in other medications and over-the-counter remedies. Cipro, Afrin, and Fluzone are often preferred since they are thimerasol-free. Women should check the ingredients of their cosmetics if they suspect a sensitivity.

Source: Medscape
Photo: Pixabay

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