Allergic Contact Dermatitis to Preservatives

Vickie L. Timm-Knudson; Janis S. Johnson; Karel J. Ortiz; James A. Yiannias


Dermatology Nursing. 2006;18(2):130-136. 

In This Article

Common Preservatives

Formaldehyde-releasing Preservatives

Formaldehyde and the formaldehyde-releasing preservatives are some of the most effective preservatives on the market (Marks, Elsher, & Deleo, 2002). They are especially effective in preventing growth of gram-negative bacteria. Formaldehyde is found in the TRUE Test, which is the common patch test panel used for screening for ACD in the United States. About 8.4% of patch test patients reported by the NACDG are sensitive to this agent (Pratt et al., 2004). Formaldehyde is widespread in the environment as a chemical byproduct produced by incomplete combustion, and it is found in cigarette smoke, car exhaust, and incineration products (Marks et al., 2002). Derivatives of formaldehyde are used as textile finishes (Marks et al., 2002). In addition to localized reactions to cosmetics containing formaldehyde or formaldehyde releasers, patients who are sensitive to these preservatives may have a more widespread eruption due to the ubiquitous use of formaldehyde derivatives (Marks et al., 2002).

Formaldehyde releasers are a diverse group of chemicals that can be recognized by a small, easily detachable formaldehyde moiety. The five most commonly used chemicals in this category are quaternium-15, dimethyl-dimethyl (DMDM) hydantoin, imidazolidinyl urea, diazolidinyl urea, and 2-bromo-2-nitropropane-1,3-diol (bronopol). Some contact allergy experts (A. Fransway, personal communication, 2005) recommend that the patient with sensitivity to only one formaldehyde releaser avoid only that particular antigen. However, when a patient is allergic to two or more formaldehyde releasers then, clearly, the patient should avoid them all. Although some experts might disagree, patients who are allergic to formaldehyde alone would be wise to avoid the formaldehyde releasers as well. CARD errs on the side of caution to the extent that if a patient is allergic to formaldehyde, formaldehyde resin, or any single formaldehyde releaser, it will generate a skin care product shopping list of items that are free of all formaldehyde-related allergens.

Because formaldehyde alone cannot adequately screen for all formaldehyde releasers, quaternium-15 is found on the TRUE Test. It is the preservative most commonly found to cause allergic reactions in the United States (Marks et al., 2002). The NACDG found 9.3% of patch test patients to be sensitive to this compound (Pratt et al., 2004). It has activity against bacteria, fungi, and molds, and it is especially effective against Pseudomonas species. Quaternium-15 is a water-soluble preservative that can effectively preserve cosmetics for as long as 2 years.

DMDM hydantoin, another formaldehyde releaser, is one of the most commonly used preservatives in cosmetics today; it caused an allergic reaction in 2.8% of the NACDG patients (Pratt et al., 2004). It is water-soluble and is found most commonly in shampoos but also in cosmetics.

The formaldehyde releaser imidazolidinyl urea is commonly used as a preservative in personal care products (for example, cosmetics and many over-the-counter medicaments). It is active against bacteria, especially Pseudomonas species, but it has less activity against fungi. To provide more broad-spectrum activity against gram-positive and gram-negative bacteria and fungi, imidazolidinyl urea is often combined with another preservative such as parabens. The NACDG found that 3% of patients reacted to this compound (Pratt et al., 2004). Imidazolidinyl urea is widely used because it is not a strong irritant and is generally well tolerated. Patients who are sensitive to formaldehyde may be able to tolerate this compound because it releases minimal formaldehyde. Diazolidinyl urea is quite similar to imidazolidinyl urea.


2-Bromo-2-nitropropane-1,3-diol (bronopol) is a formaldehyde-releasing preservative found in cosmetics and topical medicaments. It has a broad spectrum of activity against bacteria and fungi. It caused contact dermatitis in 3.3% of NACDG study patients (Pratt et al., 2004). It can be an irritant as well.


Parabens are also commonly used as preservatives in personal care items. Two or more parabens are usually combined in a product to provide a broader antiseptic action. The most common parabens in skin care products include ethyl paraben, methyl paraben, propyl paraben, butyl paraben, isobutyl paraben, and isopropyl paraben (Marks et al., 2002). These preservatives were patch tested as a mix of the first four listed parabens and caused ACD in 1% of the patients patch tested by the NACDG (Pratt et al., 2004). Parabens are not only the most commonly used preservatives in cosmetics but also can be found in pharmaceuticals and foods. In gesting foods containing parabens rarely causes an allergic reaction. This preservative is almost ideal because it is colorless, odorless, and rather nonirritating, and it also has activity against a wide range of bacteria. Parabens are less active against fungi and therefore are usually combined with another type of preservative such as a formaldehyde releaser. In a phenomenon known as the paraben paradox, inflamed skin reacts to parabens whereas intact skin does not. This concept is important because patch tests may produce false-negative findings in patients who are truly sensitive to parabens.

Kathon CG

Another commonly used preservative in skin care products and cosmetics is methyl chloroisothiazolinone and methyl isothiazolinone (Kathon CG; Rohm and Haas Company, Philadelphia, PA). It has a broad spectrum of activity and is compatible with most cosmetic formulations. It was the cause of allergic reactions in 2.3% of NACDG patients (Pratt et al., 2004). Persons allergic to Kathon CG can often tolerate rinse-off products containing the compound.


Thimerosal is a preservative used in cosmetics, topical medicaments, eye solutions, and vaccines. It induced an allergic response in 10.2% of patients tested by NACDG (Pratt et al., 2004). Thimerosal is effective against both bacteria and fungi. Vaccines containing thimerosal rarely cause a reaction in persons who are patch-test sensitive. Interestingly, patients can have a false-positive reaction to tuberculin intradermal testing preserved with thimerosal. Con junctivitis and eyelid dermatitis are common reactions in sensitive patients using eye preparations that contain thimerosal. Although thimerosal is not commonly used in skin care products, it is often found in mascara. Indeed, the decreased use of thimerosal in skin care products and the large number of nonrelevant positive reactions to thimerosal have led the NACDG to remove thimerosal from its standard patch-test series. The large number of patients sensitized to thimerosal has likely occurred because of exposure to it through vaccines preserved with thimerosal.


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