Contact allergy to a shellac-containing mouthguard.

Shellac is a typical cosmetic allergen that can cause reactions such as eyelid dermatitis to mascara or contact cheilitis to lipstick. However, in this case report we present shellac as a relevant contact allergen in a noncosmetic context.

CASE REPORT

A 21‐year‐old female, with a history of asthma, presented at our outpatient clinic as third opinion with a recurrent lower median lip fissure (Figure 1A). For 3 years she experienced fissures and dry scaling of her lower lip as well as simultaneously occurring numerous mildly painful aphthae on the labial and buccal mucosa. Prior treatment with topical corticosteroids, emollients, antifungal, and antimicrobial ointments were only moderately effective. A skin biopsy showed chronic ulcerative inflammation without specific characteristics. Additional tests ruled out herpes infections, nutritional deficiencies, and immunobullous diseases. She used the same brand toothpaste for years and denied using lip cosmetics (or any other cosmetics other than shower gel and shampoo). However, as a passionate hockey player she frequently wore a hockey mouthguard. We performed patch tests with the European baseline series, and additional series containing corticosteroids, cosmetics, plastic/glues, and rubber chemicals (van der Bend B.V., Brielle, The Netherlands). Allergens were applied to the back for 2 days with Finn Chambers (SmartPractice, Phoenix, Arizona). Readings at day (D) 2 and D3 showed only positive reactions to shellac 20% in ethanol +/+ in the cosmetic series. We weekly test this series and very rarely find a positive reaction to shellac. We then contacted the manufacturer who confirmed that her mouthguard contained shellac. Replacement by a shellac‐free mouthguard with similar design by her dentist resulted in complete remission of her symptoms within 1 month (Figure 1B).

FIGURE 1

Lower median lip fissure (A) with a complete remission of her oral symptoms within 1 month after replacement with a shellac‐free mouthguard (B)

DISCUSSION

Oral aphthae and lip fissures are common symptoms in dermatologists' daily practice. Arriving at a diagnosis can be challenging and the complaints are notoriously recalcitrant. The differential diagnoses for aphthae include viral infections, immunobullous diseases, and Morbus Behçet. Differential diagnoses for lip fissures include lip lick dermatitis, median lip fissure, or dermatitis artefacta. Patch tests can be useful to determine whether an underlying and relevant contact allergy is present or not. Eliminating the culprit allergen can completely resolve the often long‐lasting symptoms. Most underlying causative agents for lip dermatitis include lip cosmetics, toothpaste and other dental care products, metals (dental or orthodontic devices, musical instruments), food, medications, nail varnishes, and rubber gloves. , However, in our case shellac was considered a likely culprit contributing to the clinical picture.

Shellac, also known as lacca (CAS no. 9000‐59‐3), is a natural resinous secretion of the insect Laccifer lacca (Tachardia lacca), currently named Coccus lacca. , Shellac is considered a “natural plastic” and used in the food, drug, and cosmetic industries. It is applied in cosmetics for its emollient and coat‐forming characteristics. , Shellac can be found in hair sprays, lotions, shampoos, eyeliners, mascaras, nail polishes, lipsticks, and fragrances. In addition, it is used for coating or glazing of food, candies, and medicines. Furthermore, shellac is widely present in dentures and other dental products. Skin sensitization to shellac is rare. Reports of allergic contact dermatitis describe mainly eyelid dermatitis from mascara or eyeliner and contact cheilitis from lipsticks. , Patch testing is recommended with shellac 20% in ethanol. , This case report adds sport‐related mouthguards as an unusual and possibly underreported cause of contact dermatitis to shellac.

CONFLICTS OF INTEREST

None declared.

AUTHOR CONTRIBUTIONS

Koen Quint: Conceptualization (equal); data curation (equal); formal analysis (equal); funding acquisition (equal); investigation (equal); methodology (equal); project administration (equal); resources (equal); software (equal); supervision (equal); validation (equal); visualization (equal); writing – original draft (equal); writing – review and editing (equal). Esther J van Zuuren: Conceptualization (equal); data curation (equal); formal analysis (equal); funding acquisition (equal); investigation (equal); methodology (equal); project administration (equal); resources (equal); software (equal); supervision (equal); validation (equal); visualization (equal); writing – original draft (equal); writing – review and editing (equal).