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Hairdressers are commonly exposed to methylisothiazolinone at work.

More people develop allergies to common preservative in makeup and household products

 In one third of the persons tested, the allergy was linked to exposures at work.

A recent study by STAMI finds that the number of Norwegians with contact allergy to methylisothiazolinone has increased significantly since 2008.

Methylisothiazolinone (MI) is a water-soluble preservative that prevents the growth of microorganisms such as bacteria and moulds. 

It is commonly added to cosmetics, household products, and other industrial products including paints, glues, and cleaners. 

Unfortunately, MI has also been shown to have strong allergenic properties.


Methylisothiazolinone can cause a type of eczema called allergic contact dermatitis with typical inflammatory symptoms such as redness, itching, burning or a stinging sensation, swelling, blisters, crusting and peeling skin. More severe reactions, such as a rash all over the body, is also observed.

Following a change in the EU cosmetics regulations in 2016, MI is now prohibited in cosmetic products that remain on the skin. This includes creams and lotions. 

In cosmetic products that are meant to be rinsed off, like shampoos and soaps, MI is still allowed.

Lack of updated figures

In the years following the introduction of MI, there has been a sharp increase in the number of people with contact allergic dermatitis (eczema) in several countries all over the world.

However, consultant and STAMI-researcher Jose H. Alfonso and his colleagues saw that there was a lack of updated data from Norway. 

The most recent figures available were from the years 2006 to 2008, and reported a two per cent prevalence of contact allergy to MI.

“We therefore decided to do a follow-up study, to get updated figures on how many people suffer from MI-related contact allergy today,” Alfonso says.

A lot more cases

MI is either used alone or together with the related substance methylchloroisothiazolinone (MCI).

To calculate the prevalence and clinical outcome of MI/MCI, Alfonso and his colleagues examined 773 patients who underwent patch testing at the Department of Dermatology at Oslo University Hospital.

“7.1 per cent of the patients were found to have a contact allergy to MI/MCI. This is more than 3.5 times as many as 13 years ago,” the researcher says.

Most of the participants were 40 years or older. 82 per cent of those who tested positive were women, and half of the positive cases had a history of atopic dermatitis.

Occupational risk prevention needed

“Up to a third of the cases were related to occupational exposure, mainly in the form of hand eczema. The most common exposures were chemicals and coolants, hairdressing supplies and cleaning products,” Alfonso sums up.

Professional groups at risk are mechanics, painters, hairdressers, cleaners, and healthcare personnel.

The STAMI-researcher emphasises that the result may deviate somewhat from the real national prevalence. This is because the data was collected at a hospital responsible for a population of 3.1 million people, where only the most severe cases of chronic eczema are referred for assessment.

“Since a third of the cases were related to occupational exposure, targeted preventive efforts are needed to eliminate and reduce exposure to MI/MCI in working life,” Alfonso concludes.


Sidhu et al. Prevalence and clinical outcome of contact allergy to methylisothiazolinone/methylchloroisothiazolinone in Southern-East Norway: A retrospective case-studyContact Dermatitis, vol. 88, 2023. DOI: 10.1111/cod.14308

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