What is Methylisothiazolinone?

MI is methylisothiazolinone — an effective preservative, used in consumer products such as toiletries, cosmetics, baby wipes and household cleaning products to prevent the growth of bacteria and moulds in the products, and thereby extend their shelf life and usage. 

A related preservative — methylchlorisothiazolinone or MCI — is also used in cosmetics, but only in a blend with MI, sometimes called Kathon CG, which is a mixture of three parts MCI to one part MI. MCI cannot be used in cosmetics on its own without MI. 

Both MI and MCI may also be found in household cleaning products, such as fabric conditioners and washing up liquids, but should in these cases be labelled. Such products may also use other types of isothiazolinones, such as benzisothiazolinone and octylisothiazolinone.

Household paints may also contain all these preservatives, but paints are not required to be labelled with ingredients in the EU. 

Use of MI

The use of MI has increased in cosmetics over the last 10 years. There appear to have been two reasons for this:

1. Concern over a class of preservatives called parabens, the use of which some have suggested could increase the risk of breast cancer, although this has not been scientifically proven. In seeking to avoid using parabens, alternative preservatives have been sought out by many manufacturers — among them MI.

2. Earlier concern about the safety of MCI resulted in a reduction in use of the MI/MCI blend, meaning that some manufacturers chose to use MI only, and sometimes in higher concentrations. 

Allergy to MI

Allergies in general have been on the increase worldwide for many years, and in line with this rise in reactions to foods, pollens, dust mites, fragrances and other allergens, allergy to methylisothiazolinone has also risen, also because of its increased popularity in formulations.

However, in more recent years, MI allergy has been a particular problem, so much so, that in 2013, the American Contact Dermatitis Society voted it ‘Allergen of the Year’. 

For more on Allergy to MI and diagnosis of MI allergy, see MI Allergy Diagnosis


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