Shellac is a resin obtained from the female lac insect, predominantly found in India and Thailand. Upon exposure to air, it solidifies and is typically processed into amber flakes for commercial purposes. This resin has diverse applications, including its use in cosmetics, household products, and as a food glaze. It is distinct from ‘Shellac nails’, which refers to a specific brand of gel nail polish.

In the realm of cosmetics, shellac is incorporated into products such as mascara, nail polish, lipstick, and hairspray. It also finds its way into household items like paint primers and wood sealants. Additionally, shellac is utilized in food and pharmaceutical industries for coatings on candies, tablets, and as a binding agent in dentures. 

Patch testing shows that reaction rates to shellac vary between 2–10%, and since the product is tested in 20% alcohol, some reactions could be of an irritating nature rather than allergic.

Individuals with a contact allergy to shellac typically experience contact dermatitis in areas where they have been exposed to the product. For instance, eyelid dermatitis may occur from mascara, or lip inflammation (cheilitis) from lipstick use. The symptoms of allergic contact dermatitis usually manifest as redness and swelling, which can escalate to blister formation in severe cases.

Diagnosing a shellac contact allergy involves a combination of examination, patient history, and skin patch testing. A positive reaction may be evident at the application site during readings taken at 48 or 96 hours.

To prevent further allergic reactions, it is crucial for those with a shellac allergy to strictly avoid products containing this resin. Treatment of the resultant contact dermatitis may require the use of emollients and topical corticosteroids until the inflammation subsides. For more detailed treatment information, refer to the post about allergic contact dermatitis.

It is vital for individuals to meticulously review the ingredient lists of products they currently use or intend to purchase to identify the presence of shellac. Products to be avoided include those labeled with terms such as Candy glaze, Confectioner’s glaze, Gomme laque, Lac resin, Lacca, Schellack, Shellac (purified), Shellac glaze, and Shellac orange S-40.