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Author: Dr Leah Jones, Registrar, Waikato District Health Board, New Zealand. Copy edited by Gus Mitchell. December 2021.
Shellac is a resin produced from the female lac insect found in India and Thailand. It hardens on exposure to air and is often manufactured into amber flakes for sale. It is commonly used in cosmetics, furniture sealants, and as a food glaze. It should not be confused with ‘Shellac nails’ — a brand of gel nail polish.
Shellac can be found in:
The reaction rate with patch testing varies between 2–10%. Given the product is tested in 20% alcohol, some of the reactions may be irritating in nature.
Patients with a contact allergy to shellac will present with contact dermatitis on areas exposed to the product, such as eyelid dermatitis in the case of mascara or lip inflammation (cheilitis) from lipstick.
The allergic contact dermatitis commonly presents as erythema and swelling, but may progress to the development of blisters in severe reactions.
Shellac contact allergy can be diagnosed through examination, history taking, and skin patch testing. A positive reaction may be seen over the site of application during the 48 hour or 96 hour reading.
Strict avoidance of products containing shellac is necessary to prevent further reactions. The resultant contact dermatitis may need treatment with emollients and topical corticosteroids until the inflammation resolves. See allergic contact dermatitis for further information on treatment.
It is important to carefully inspect the ingredients list of any products currently being used or prior to purchase to identify products containing shellac.
Products containing the following should be avoided:
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