Stewart C, Parker JA, Hwang R, Vincent M, Fung ES. Quantitative risk assessment of skin sensitization elicitation following use of shampoo products containing formaldehyde-releasing preservative DMDM hydration. Poster presentation P519 at the Society of Toxicology (SOT) Annual Meeting & ToxExpo, San Diego, CA. Toxicologist 186(S1):148. Abstract 3330. March 2022.
Preservatives are routinely used in personal care products, including shampoos, to extend their shelf-life. While the use of formaldehyde has been phased out due to skin sensitization potential, formaldehyde-releasing preservatives, such as DMDM hydantoin (DMDMH), are still widely used. A relationship has been established between positive patch test results following exposure to DMDMH and previous sensitization to formaldehyde. Recently, there have been reports of hair loss following use of certain shampoo products containing DMDMH. Hair loss is a multifaceted condition that can be caused by a variety of factors; while the mechanism is unclear, immune-related conditions have been reported to contribute to hair loss. The aim of this analysis was to conduct a quantitative risk assessment to assess the risk of skin sensitization elicitation following use of shampoo products that contain the maximum allowable concentrations of DMDMH in formulation (1% w/v). Up to 2% of free formaldehyde is found in equilibrium with DMDMH, thus, 0.02% formaldehyde concentration in shampoo was assumed. In order to determine a margin of safety (MOS) for exposure to DMDMH from use of shampoo products, consumer exposure levels (CEL) were estimated based on typical use scenarios (1.11 applications/day; 10 mg shampoo/cm2/application) and then benchmarked against an acceptable exposure level (AEL). The AEL was derived using a weight of evidence approach where a range of no expected sensitization induction levels (NESILs) was utilized, including one generated using benchmark dose modeling, to account for variability in individual susceptibility. The resulting MOS values for a shampoo product containing 1% DMDMH (0.02% formaldehyde) was above 1 for the typical use scenario outlined above indicating there is a low likelihood of skin sensitization elicitation among individuals expected to be otherwise healthy. Given these results, it can be concluded that shampoo products containing DMDMH at or below current allowable concentrations are not expected to increase the risk of skin sensitization elicitation. More importantly, these methods can be applied to future studies examining skin sensitization elicitation following exposure to other formaldehyde-releasing preservative.