Merthiolate, thiomersalatem, sodium ethylmercury salicylate — thimerosal. This organic mercury is a top contact allergen and had a long history of safety and efficacy as a preservative. But, due to concerns about exposure to mercury-containing ingredients, it is now less commonly found.
Thimerosal used to be a staple antiseptic, antibacterial, and antifungal as an ingredient in popular antimicrobial products as well as on its own (remember tincture of merthiolate?). It was regularly found in medical preparations such as opthalmogic ointments, topical pharmaceutical medications, vaccines, prick test allergens, immunoglobulins, and antitoxins. It was also used as a preservative in cosmetics (especially in products used around the eye like mascaras, eyeshadows, makeup removers, and eye serums). Some eye solutions still contain thimerosal, a mercuric derivative of thiosalicylic acid. It is also still found in some vaccines and tattoo inks. It may cross react with mercury which is sometimes used as a preservative in shoe manufacturing.
Mercury is a well studied environmental pollutant that gets into the soil from atmospheric or from biological and chemical processing. This is highest in tropical areas without much vegetation, lower in temperate zones, and lowest at the poles.
If you’ve patch tested positive to thimerosal, avoid it in the products that you use. Read the ingredients carefully. It can also appear as these other names:
- Sodium ethylmercurithiosalicylate
- Ethyl (2-mercaptobenzoato-S) mercury sodium salt
- [(o-carboxyphenyl)thio] Ethylmercury sodium salt
If you need a vaccine that has no thimerosal-free alternative, discuss the risks and benefits with your doctor. An allergic reaction may be mild and fleeting or otherwise less risky than the potential illness that the vaccine protects you against.
If you have a history of sensitive skin…
…don’t guess! Random trial and error can cause more damage. Ask your dermatologist about a patch test.
To shop our selection of hypoallergenic products, visit vmvhypoallergenics.com. Need help? Ask us in the comments section below, or for more privacy (such as when asking us to customize recommendations for you based on your patch test results) contact us by email, or drop us a private message on Facebook.
- On the prevalence of skin allergies, see Skin Allergies Are More Common Than Ever.
- For the difference between irritant and allergic reactions, see It’s Complicated: Allergic Versus Irritant Reaction.
- For the difference between food, skin, and other types of reactions: see Skin & Food Allergies Are Not The Same Thing.
- On the differences between hypoallergenic, natural, and organic, check out Is Natural Hypoallergenic? and this video in our YouTube channel.
- To learn about the VH-Rating System and hypoallergenicity: What Is The Validated Hypoallergenic Rating System?
Regularly published reports on the most common allergens by the North American Contact Dermatitis Group and European Surveillance System on Contact Allergies (based on over 28,000 patch test results, combined), plus other studies. Remember, we are all individuals — just because an ingredient is not on the most common allergen lists does not mean you cannot be sensitive to it, or that it will not become an allergen. These references, being based on so many patch test results, are a good basis but it is always best to get a patch test yourself.
- DeKoven JG, Silverberg JI, Warshaw EM, Atwater AR, et al. North American Contact Dermatitis Group Patch Test Results: 2017-2018. Dermatitis. 2021 Mar-Apr 01;32(2):111-123.
- DeKoven JG, Warshaw EM, Zug KA, et al. North American Contact Dermatitis Group Patch Test Results: 2015-2016. Dermatitis. 2018 Nov/Dec;29(6):297-309.
- DeKoven JG, Warshaw EM, Belsito DV, et al. North American Contact Dermatitis Group Patch Test Results 2013-2014. Dermatitis. 2017 Jan/Feb;28(1):33-46.
- Warshaw, E.M., Maibach, H.I., Taylor, J.S., et al. North American contact dermatitis group patch test results: 2011-2012. Dermatitis. 2015; 26: 49-59.
- W Uter et al. The European Baseline Series in 10 European Countries, 2005/2006–Results of the European Surveillance System on Contact Allergies (ESSCA). Contact Dermatitis 61 (1), 31-38.7 2009.
- Wetter, DA et al. Results of patch testing to personal care product allergens in a standard series and a supplemental cosmetic series: An analysis of 945 patients from the Mayo Clinic Contact Dermatitis Group, 2000-2007. J Am Acad Dermatol. 2010 Nov;63(5):789-98.
- Warshaw EM, Buonomo M, DeKoven JG, et al. Importance of Supplemental Patch Testing Beyond a Screening Series for Patients With Dermatitis: The North American Contact Dermatitis Group Experience. JAMA Dermatol. 2021 Dec 1;157(12):1456-1465.
- Verallo-Rowell VM. The validated hypoallergenic cosmetics rating system: its 30-year evolution and effect on the prevalence of cosmetic reactions. Dermatitis 2011 Apr; 22(2):80-97.
- Ruby Pawankar et al. World Health Organization. White Book on Allergy 2011-2012 Executive Summary.
- Misery L et al. Sensitive skin in the American population: prevalence, clinical data, and role of the dermatologist. Int J Dermatol. 2011 Aug;50(8):961-7.
- Warshaw EM1, Maibach HI, Taylor JS, Sasseville D, DeKoven JG, Zirwas MJ, Fransway AF, Mathias CG, Zug KA, DeLeo VA, Fowler JF Jr, Marks JG, Pratt MD, Storrs FJ, Belsito DV. North American contact dermatitis group patch test results: 2011-2012.Dermatitis. 2015 Jan-Feb;26(1):49-59.
- Warshaw, E et al. Allergic patch test reactions associated with cosmetics: Retrospective analysis of cross-sectional data from the North American Contact Dermatitis Group, 2001-2004. J AmAcadDermatol 2009;60:23-38.
- Foliaki S et al. Antibiotic use in infancy and symptoms of asthma, rhinoconjunctivitis, and eczema in children 6 and 7 years old: International Study of Asthma and Allergies in Childhood Phase III. J Allergy Clin Immunol. 2009 Nov;124(5):982-9.
- Kei EF et al. Role of the gut microbiota in defining human health. Expert Rev Anti Infect Ther. 2010 Apr; 8(4): 435–454.
- Thavagnanam S et al. A meta-analysis of the association between Caesarean section and childhood asthma. Clin Exp Allergy. 2008;38(4):629–633.
- Marks JG, Belsito DV, DeLeo VA, et al. North American Contact Dermatitis Group patch-test results, 1998 to 2000. Am J Contact Dermat. 2003;14(2):59-62.
- Warshaw EM, Belsito DV, Taylor JS, et al. North American Contact Dermatitis Group patch test results: 2009 to 2010. Dermatitis. 2013;24(2):50-99.
- Verallo-Rowell V. M, Katalbas S.S. & Pangasinan J. P. Natural (Mineral, Vegetable, Coconut, Essential) Oils and Contact Dermatitis. Curr Allergy Asthma Rep 16,51 (2016) . https://doi.org/10.1007/s11882-016-0630-9.
- Park G, Oh DS, Lee MG, Lee CE, Kim YU. 6-Shogaol, an active compound of ginger, alleviates allergic dermatitis-like skin lesions via cytokine inhibition by activating the Nrf2 pathway. Toxicol Appl Pharmacol. 2016 Nov 1;310:51-59. doi: 10.1016/j.taap.2016.08.019. Epub 2016 Aug 22. PMID: 27562088.
- de Groot AC. Monographs in Contact Allergy, Volume II – Fragrances and Essential Oils. Boca Raton, FL: CRC Press Taylor & Francis Group; 2019.
- De Groot AC. Monographs in Contact Allergy Volume I. Non-Fragrance Allergens in Cosmetics (Part I and Part 2). Boca Raton, Fl, USA: CRC Press Taylor and Francis Group, 2018.
- Zhu TH, Suresh R, Warshaw E, et al. The Medical Necessity of Comprehensive Patch Testing. Dermatitis. 2018 May/Jun;29(3):107-111.
Want more great information on contact dermatitis? Check out the American Contact Dermatitis Society, Dermnet New Zealand, the Contact Dermatitis Institute, and your country’s contact dermatitis association.
Laura is our “dew”-good CEO at VMV Hypoallergenics and eldest daughter of VMV’s founding dermatologist-dermatopathologist. She has two children, Madison and Gavin, and works at VMV with her sister CC and husband Juan Pablo (Madison and Gavin frequently volunteer their “usage testing” services). In addition to saving the world’s skin, Laura is passionate about health, inclusion, cultural theory, human rights, happiness, and spreading (like a VMV cream!) goodness!