Methylisothiazolinone Allergy – Symptoms and Diagnosis

If you suspect you have an allergy to MI, do not self-diagnose. It is very easy to get this wrong, as most cosmetics contain dozens of ingredients, any of which could be causing reactions and symptoms. Any problem may also be related to something else — such as clothing or bedding, or a food sensitivity. 

Symptoms of MI Allergy

These include:

  • Redness and rashes
  • Inflammation
  • Itchiness and irritation
  • (Longer term) Scaly, flaky skin

These may be found anywhere on the body, but sites typically affected by MI allergy include the fingers and hands, around the eyes, or in the nappy area of babies. 

However, it’s important to note that these symptoms may relate to allergies to other ingredients in cosmetics, such as fragrances, essential oils and other preservatives, as well as non-allergic irritant reactions to both ingredients and other materials to which the skin has come into contact.

Diagnosis of MI Allergy

See your doctor in the first instance.

It can help if you first keep a daily diary — both of products you use or come into contact with, and the emergence of symptoms. Note how severe they are and where on the body they occur. 

Your doctor will examine you and may refer you for patch testing with a specialist skin doctor, called a dermatologist. 

This involves placing adhesive ‘patches’ — containing small amounts of various potential allergy-triggering ingredients — onto your skin (usually on your back), for several days. After several days, the patches are removed, and the skin examined for any reaction or response, such as inflammation or redness. 

This can help identify an allergy not only to MI and related preservatives, but to other potentially problematic ingredients which come into contact with your skin, such as fragrance compounds. 

MI Allergy Management

If you are diagnosed with MI, you will have to scrutinise all cosmetic and household product labels for the ingredient methylisothiazolinone and methylchloroisothiazolinone — although the latter will not appear without the former in the case of cosmetic products. 

Household cleaning products may also contain other isothiazolinone compounds, such as benzylisothiazolinone. 

Note that some products, such as household paints, are not required to declare ingredients, so you must check with manufacturers whether the preservatives are used. Most well known and ‘high street’ brands do use isothiazolinones to preserve their paints and varnishes. 

For suggestions of MI-free products, choose the relevant category from the Cosmetics or Household drop-down options on the menu at the top of the page.

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