The most common symptom of an allergy or reaction to themirosal, an ingredient found in vaccines and other drugs, is redness or swelling at the site of the injection, notes the Centers for Disease Control. When treated with topical creams, the reaction generally resolves within one to two days.
Themirosal, a naturally occurring mercury compound used as a preservative in vaccines and other drugs, can cause mild allegic reactions. Topical cortisol creams can treat themirosal reactions. As of 2015, there is no research to indicate that themirosal causes autism or any other neuropsychological problems, according to the CDC.
A skin patch test using 0.1 percent themirosal in aqueous solution determines themirosal sensitivity, reports DermNet NZ. Because of safety concerns about themirosal, many vaccines have removed it from their formulas. A complete list of vaccines containing themirosal is available on the CDC's website.