Dear members,

This month, we feature three summaries of recent publications covering MCI/MI exposure in cosmetics, patch testing for dental material allergy, and the prevalence of alkyl glucosides in cosmetic products:

Methylisothiazolinone 10 Years After Regulation: A Case Story of Liquid Soaps and Shampoos

Pedersen MK, Schwensen JFB, Alfonso JH et al. Contact Dermatitis. 2026 Jun 16. doi: 10.1111/cod.70202. PMID: 42300206.

Pedersen et al. investigated the use of MCI/MI in marketed cosmetics10 years after EU regulatory changes. From a Danish database, 257 (2.5%) products containing MCI/MI or MI were identified, most commonly shampoos and conditioners. Chemical analysis (LC-MS/MS) was performed on 30 rinse-off products. While most complied with current legislation, two liquid hand soaps exceeded the permitted 15 ppm concentration, and four products did not meet the required MCI:MI ratio (3:1). However, only products declaring MCI/MI or MI were included in the chemical analyses. Despite a marked reduction in overall use compared with the pre-regulation era, MCI/MI remains a clinically relevant allergen. The findings raise questions about whether the current 15 ppm limit is sufficiently protective, particularly for frequently used rinse-off products such as hand soaps, and support continued compliance monitoring, surveillance, and more proactive approaches to preservative risk assessment and management.

Patch Test Reactions to Dental Materials: A Retrospective Single-Centre Study

Bizjak-Suran M, Marčun M, Košnik M, Dinevski D. Contact Dermatitis. 2026 Jun 16. doi: 10.1111/cod.70205. PMID: 42301131.

Bizjak-Suran et al. retrospectively analysed 439 adults referred for suspected dental material allergy who underwent patch testing with a local 24-allergen dental series. Half of patients had at least one positive reaction, with metals predominating. Nickel (23.0%) and palladium (16.6%) were the most common allergens. Methacrylate allergy was less frequent (6.2%) but reliance on HEMA alone would have missed over 40% of methacrylate-positive patients, with HPMA providing important additional diagnostic yield. Tin was not included in the series. Notably, almost 19.8% reactions were detected only on day 6/7. The findings support comprehensive dental series and suggest late readings detects additional sensitized patients.

Alkyl Glucosides in Rinse-Off and Leave-On Cosmetics Available on the Dutch Market

Yaâkoubi M, Ipenburg NA, Groot AC, Rustemeyer T. Contact Dermatitis. 2026 Jun 14. doi: 10.1111/cod.70200. PMID: 42289776.

In this Dutch study, 650 cosmetic products were assessed for the presence of alkyl glucosides. Nearly half (47.3%) of rinse-off products contained at least one alkyl glucoside, particularly baby shampoos, shower gels and baby shower gels (56–62%), while around one in five leave-on products (excluding lip balms) also contained these ingredients. Coco-glucoside predominated in rinse-off formulations, whereas cetearyl glucoside was most common in leave-on products. Given the substantial co-reactivity between alkyl glucosides, the authors suggest that sensitised patients avoid all products containing this class of surfactants. The findings reinforce the importance of checking ingredient labels and considering alkyl glucosides in patients with persistent cosmetic-related allergic contact dermatitis.