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Author: Dr Selene Ting, Dermatology Advanced Trainee, Auckland District Health Board, Auckland, New Zealand. Copy edited by Gus Mitchell. November 2021
Octylisothiazolinone (OIT), whose active ingredient is 2-Octyl-2H-isothiazol-3-one, is a type of isothiazolinone preservative, which can cause allergic contact dermatitis. It is a biocide typically added as a film preservative to protect surfaces or the final coating of manufactured products, in order to prevent growth of bacteria, moulds, and fungi.
OIT shares similar chemical characteristics to other isothiazolinones. It has moderate sensitisation potency, which can produce skin irritations and allergies.
OIT can be found in many commercial household and industrial products such as:
Methylisothiazolinone (MI) is a related allergen which may show immunologic cross-reactions to octylisothiazolinone. MI has been found to cause high rates of contact allergic dermatitis and was declared the Contact Allergen of the year for 2013 by the American Contact Dermatitis Society.
Anyone with exposure to octylisothiazolinone can become sensitised and develop subsequent contact allergy. People with contact allergy to methylisothiazolinone or other types of isothiazolinone can also react to OIT. Most cases of reported allergic contact dermatitis from OIT are in occupational settings.
Some of the common occupations implicated include:
There is an increasing frequency of non-occupational contact dermatitis cases described due to its increased use in the leather and textile industry in particular.
Sensitised individuals will develop contact dermatitis on exposure to OIT when it comes in contact with their skin.
Sites involved include:
The rash may be:
Patch testing confirms the diagnosis. OIT is one of the allergens in the cutting oils patch test series. The patch test material is applied to the patient’s back, with test results being read at day 2 and day 5 after application of the allergens.
Once OIT sensitivity is confirmed, it is important to avoid exposure to any products containing OIT. The dermatitis is treated as for any acute dermatitis, by application of a topical corticosteroid and an emollient until the allergic reaction settles. An antihistamine can be used for itch. Use a soap substitute.
It is essential to avoid contact with products which contain OIT, or other isothiazolinone preservatives, especially MI, as there may be a risk of cross-reactivity. Read product labels to check the ingredients.
Employers should be informed of the allergy in order to avoid exposure to OIT if the source of the contact allergy is work-related. If this is not possible, then use practical measures such as protecting the skin with gloves to minimise exposure. Potential sources of exposure can be identified using Material Safety Data sheets.
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