A dedicated session at the 2025 Dermatology Days of Paris conference, held from December 2 to 6, 2025, in Paris, France, focused on contact allergens that clinicians should recognize in everyday practice. A series of speakers reviewed newly identified allergens and explained their relevance to routine dermatological care.
“I have prepared a selection of practical points to know about recently identified allergens,” said Emmanuelle Amsler, MD, dermatologist and allergologist at Assistance Publique-Hôpitaux de Paris (AP-HP), Hôpital Tenon, Paris, France, in her introduction.
Allergies Linked to Headphones
Two allergens were highlighted: octylisothiazolinone and dimethyl fumarate. Octylisothiazolinone is a biocide used in leather, synthetic leather, and headphone foams. Although prohibited in cosmetics, it is known to cause severe reactions, such as edema and eczema. In several reported cases, it caused inflammatory eczema around the ears.
Dimethyl fumarate, an antifungal agent previously used in sofas, was recently identified in a case related to the use of headphones. “For earphones such as AirPods, cases of allergic eczema have been reported, often linked to silicone tips or plastic components. Apple acknowledges the possible presence of nickel and acrylates in its products, which are two well-known allergens,” Amsler said.
Allergies Linked to Leather Chairs, Sofas, and Car Seats
In addition to headphones, octylisothiazolinone is found in leather chairs and car seats and has been associated with eczema at sites of direct skin contact, particularly on the back of the body. A more recently recognized substance, 2-(thiocyanomethylthio)benzothiazole, an antibacterial and antifungal agent used in leather, was identified as the cause of several cases reported in Belgium between 2019 and 2022.
Allergies Linked to Watches and Mobile Phones
In smartwatches, nickel remains a well-recognized contact allergen and is found in clasps or beneath the silicone components of the devices. Protective screens containing acrylates such as isobornyl acrylate and 4-acryloylmorpholine have also been associated with eczema.
Allergies Linked to Orthopedic Implants
Annick Barbaud , MD, PhD, professor of dermatology and head of the Department of Dermatology and Allergology at AP-HP, Hôpital Tenon, Sorbonne Université, presented findings from a multicenter study conducted by the Dermato-Allergology Group of the French Society of Dermatology on metal hypersensitivity in orthopedic implants, particularly knee prostheses.
Orthopedic surgeons sometimes encounter unexplained postimplantation pain, particularly in knee prostheses. When no other cause is identified, delayed metal hypersensitivity is suspected in approximately 5% of cases, often in the context of an aseptic lymphocyte-dominated vasculitis-associated lesion, as noted by Barbaud.
The study included 253 patients with prosthesis intolerance, mostly older women with knee implants. Nearly half of the patients were sensitized to at least one metal, including 31% who were sensitized to nickel. Sensitization to cobalt was also more frequent in 10% of patients than in the general population. Allergic reactions to cement components, including acrylates and methyl methacrylate, are rare and far less frequent than those reported in previous studies. Sensitization to titanium and manganese was observed in 4% and 2% of patients, respectively.
Barbaud recommended the following approach:
- Allergy workups should be conducted only in cases of postimplantation intolerance.
- Limit testing to key metals nickel, cobalt, chromium, and titanium, along with cement components such as gentamicin, 2-hydroxyethyl methacrylate (HEMA), and methyl methacrylate.
- When titanium hypersensitivity is suspected, it is important to assess several titanium salts and prioritize patch testing over expensive in vitro assays.
Allergies Linked to Nail Products
Camille Leleu, MD, Department of Dermatology, Centre Hospitalier Universitaire Dijon, Dijon, France, focused on allergic risks associated with nail products, particularly artificial nails and permanent nail polish. Her presentation was based on an analysis of 214 TikTok videos of nail product allergies.
“Among the clinical cases was a 16-year-old girl with severe eczema triggered by repeated use of semipermanent nail polish at home. Testing revealed multiple sensitizations to acrylates, particularly 2-hydroxyethyl methacrylates,” Leleu said.
A retrospective study from Amsterdam involving 2927 individuals showed that 1.5% were sensitized to HEMA, predominantly women, with either occupational or nonoccupational exposure. Cosmetic nail products were the most common cause. This is despite EU legislation restricting the use of HEMA and other acrylates in nail cosmetics to professional use only, with mandatory labeling since November 2020.
“A new HEMA-free label has been introduced, but it does not address the problem because individuals sensitized to other acrylates can still experience severe reactions. For example, a 22-year-old woman developed severe edema despite using HEMA-free labelednail polish,” Leleu added. She concluded by emphasizing the importance of informing patients about the risks associated with the use of nail products.
This story was translated from Univadis France, part of the Medscape Professional Network.
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