Named ‘Allergen of the Year’ in 2013, methylisothiazolinone is a preservative which has caused an epidemic of allergic disease worldwide. Used in cosmetics, household detergents and paints, MI – as it is more commonly known – is a powerful sensitizer to which up to 10% of people with eczema and 1.5% of the population may react, often severely.

In the first book of its kind, “Living with Methylisothiazolinone Allergy, The Complete Guide” allergy writer Alex Gazzola tells you everything you need to know about allergy to both MI and related isothiazolinone preservatives, covering testing and diagnosis, safe cosmetics, safe household products, tips on avoiding exposure, treating and managing reactions, medications, and looking after your physical and psychological wellbeing.

Here are some edited extracts from the book, covering symptoms, diagnosis and safe products.

What is MI?
MI is methylisothiazolinone — an effective synthetic preservative, used in consumer products such as toiletries, cosmetics and baby wipes to prevent the growth of bacteria and molds, thereby extending products’ shelf life and usage, and protecting consumers against exposure to harmful organisms.

A related preservative — methylchloroisothiazolinone, or MCI — is also used in cosmetics, but usually only in a blend with MI, sometimes called Kathon CG (CG stands for ‘cosmetic grade’), which is a mixture of three parts MCI to one part MI. MCI cannot be used in cosmetics independently of MI, at least in Europe.

MI and MCI are typically used in water-containing products, such as lotions or gels. (Water normally goes by the name ‘aqua’ in lists of ingredients, and is often named first.)

Both MI and MCI may also be found in many household products, such as fabric conditioners and dishwashing liquids, where they are usually labelled or declared. Such products may also contain other types of so-called isothiazolinones, such as benzisothiazolinone (BIT) and octylisothiazolinone (OIT), which are increasingly common members of the same ‘family’.

Household paints are very likely to contain several isothiazolinones, but paints are generally not required to be labelled with ingredients unless present above a certain threshold level.

Symptoms of MI allergy
There are many potential symptoms, and those with allergy to MI and related isothiazolinones will experience one or more of them, but not necessarily all.

It will vary depending on the type of exposure and the individual. No two people’s experiences are ever exactly alike, and the degree of severity will also differ.

Time of onset following exposure can also vary: from a number of hours to a few days. Symptoms can persist for many weeks. They include:

  • redness / rashes;
  • inflammation;
  • itchiness / irritation;
  • stinging;
  • swelling (eg of eyelids);
  • blistering / pustules;
  • scaly and flaky skin.

These symptoms of eczema and dermatitis can appear anywhere on the body, but sites typically affected include the fingers and hands, around the eyes and mouth, and in babies, the diaper area. These tend to be the areas where most cosmetics are handled, used or applied — as well as parts of the body regularly touched by the hands.

Because the isothiazolinones are volatile, they can become airborne — for instance, from paint applied to walls, as it dries and off-gases or vaporises, but also from surface tops wiped with detergent — and subsequent inhalation and exposure can also trigger unpleasant symptoms, especially in those with other allergic diseases such as asthma.

As well as symptoms of the skin, others reported include nausea, headaches, stinging in the eyes, muscular spasms and neurological (nerve) pain.

It’s important to recognize that all these symptoms can also be symptoms of other allergies, and in some cases of other conditions. To be sure, you must undergo skin patch testing

Patch testing
This is a specialist medical procedure used to investigate whether any skin-based symptoms you are experiencing might be aggravated or caused by an allergy to a substance to which it is being exposed.

The exposure can come through cosmetics, toiletries, household detergents and other domestic products, as well as clothing, pollen, pollutants, or other materials in your daily environment, such as leather, metal, rubber, plastics and so on.

Patch testing is conducted by dermatologists, allergists and dermatological nurses, and its aim is to discover the exact causes of your symptoms — whether or not they are due to allergy, and if so, what the triggers might be.

Anyone can undergo patch testing, but there are some contra-indications — that is, if you are pregnant or breastfeeding, have severe eczema on your back, are taking immuno-suppressant medication, or taking certain steroids.

What is involved?
The patch testing process itself involves applying small amounts of substances to your skin, usually along the top of your back, in the form of small discs or patches infused with the test substances, and which are fixed in place with medical tape.

You will be asked to not expose your back to the sun or a sun-lamp for several weeks before your first appointment. Men with hairy backs may be wise to carefully shave the day before their appointment, which can also mean eventual patch removal is less painful. Waxing should be avoided.

Anything from around twenty to over a hundred substances may be tested, depending on your particular circumstances and the chemicals you may regularly be exposed to. Usually, a set ‘baseline’ series will be applied to all patients, plus others which are specific and appropriate to you, as an individual. The patches themselves will be aligned in one or more grids and marked carefully with inks on your back in order to identify each potential allergen.

You should wear these for two days, or as long as directed, ensuring you keep your back completely dry. Exercise and sun exposure are best avoided too — sweating can loosen the adhesives.

After two days, you will be asked to attend a second appointment, and the patches will be removed and sites examined. Another two days later, you will be asked to attend a third appointment and your dermatologist will further examine all the patch sites for potential allergies.

Results can only be interpreted reliably by experienced dermatologists.

Many reactions will be negative. Do not be despondent if all tests are negative. This is still a useful result, which will bring your doctors a step closer to identifying what the actual causes or culprits are. Some may be uncertain. Some may be due to irritation, rather than allergy — in other words, your skin may respond to a substance simply because it doesn’t ‘like’ being exposed to it for four days, but not because it is allergic, or would react to it under normal circumstances, or with a fleeting exposure. Essentially, an irritant reaction is one which is prominently symptomatic after 48 hours, but resolves noticeably after 96 hours.

But one or more may be positive — be it weakly, strongly, or extremely positive. Positive allergic reactions show up as elevated pink or red patches, and the stronger ones may be blistered. An allergic reaction is likely to be more severe after 96 hours than it is at 48 hours, as it is slower to develop. Your dermatologist will probably make a firm diagnosis of allergic contact dermatitis, or allergic contact eczema — be it to MI / MCI and/or to other chemicals or substances.

If you receive a diagnosis of MI / MCI allergy (and perhaps additional allergies to other ingredients) most of the advice you will be given will focus on avoidance.

You will probably be given a leaflet or short guide, which will contain basic information, but is unlikely to cover all aspects you need to consider in the longer-term.

Some doctors will give you lists of products, but always check in case of recent ingredient changes.

Your dermatologist may also prescribe some short-term medications if your ACD is severe: these may include steroids and immuno-suppressants to treat existing symptoms and any additional ones which developed as a result of patch testing. Always double-check that any topical treatments are free of your newly-discovered allergens!

You should also receive some advice on looking after your skin: good skin care will focus on regularly using safe emollients (moisturizers) and skin protection. In the UK and EU, all leave-on emollients are MI- and MCI-free, but this is not yet the case in North America, Australia and New Zealand, for example. It may not be necessary to completely overhaul your skincare or beauty routine, but some products may well have to go.

The good news is that you are now armed with information to address the causes of the problems, and relieve the symptoms.

Safe Products
Safe product lists are kept regularly updated on the website.

Many, but not all, ‘green’ or ‘natural’ cosmetics brands avoid using MI and MCI, and other brands, such as The Body Shop, also have a policy of avoiding them. In cosmetics, you will tend to find MI and MCI in cheaper products (such as shower gels and shampoos), often supermarket own-brands, for instance.

For a list of safe cosmetic brands, click here.

With regard to household detergents, again the more natural or ‘eco’ brands are more likely to be safe, and supermarket or high street brands often unsafe.

To browse safe household products, click here.

With paints, there are far fewer options, as isothiazolinone preservatives are used in around 95%+ of paints.

For a small list, click here.

Living with Methylisothiazolinone Allergy: The Complete Guide by Alex Gazzola is available from Amazon, in paperback at £7.49 or in Kindle format £5.08.

This is an edited summary of the article which first appeared in Allergy Newsletter No. 125 Spring 2019.