Signs and Symptoms of an Allergy to Thimerosal

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Signs and Symptoms of an Allergy to Thimerosal
Vaccines often contain thimerosal. (vaccine image by Mykola Velychko from

Thimerosal is a preservative often added to vaccines to help kill bacteria. It is also known as sodium ethylmercurithiosalicylate, and may be found in low concentrations in cosmetics and a variety of topical and oral medications. While incidences of thimerosal allergy are very low, it can cause adverse reactions in some people, and these symptoms may not occur the first, second or even tenth time that you are exposed to this compound. Knowing the signs and symptoms of an allergy to thimerosal can help you avoid irritating or even serious complications in the future.

Site Reactions

Generally, the only evidence of a thimerosal reaction will be localised to the site of the injection or application of the product containing the compound. In most cases the injection site may swell slightly and redden, creating a bump that not only looks like a mosquito bite but may also itch like one. The symptoms may persist for several hours or a few days, and then fade.

Dermatological Reactions

In some cases, patients may develop an itchy, flaky, red rash after being exposed to thimerosal. In these cases the rash, which looks like eczema or dermatitis, may become infected and inflamed if the area is constantly irritated. This is particularly an issue when the subject has used cosmetics containing the compound or if the subject already has periorbital dermatitis, red, flaky, inflamed skin in the area immediately adjacent to the eyelids and sometimes occurring on the eyelids themselves.

Systemic Reactions

Systemic reactions to thimerosal are very rare. However, if you experience coughing, nausea, respiratory distress or swelling of the tongue following an injection containing thimerosal, contact your physician and go to the nearest emergency room immediately. Regardless of whether thimerosal is the ultimate culprit, these types of reactions are often fatal if left untreated.

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