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.
*I am so sorry that the text is so complex to read, my goal is really to make science accessible to EVERYONE so here is a simpler text that goes a bit less in depth