The Science Behind the Itchy M’s: Methylchloroisothiazolinone and Methylisothiazolinone

What are the Itchy M's and how do I deal with this itchy scalp?! Find out everything you need to know!

My Beautiful #RedCarpetCurlsRoyalty,

The Curly Girl Method is truly a long-haul journey for that question for perfect hair days. The journey can get confusing and overwhelming at times but that is why you have me here, to hold your hand through it all and bring you to the promised land…or should I say promised hair days? Eh? We’ll work on that.

Today’s article is one that often seems to slide under everyone’s radar, and many times is the cause for those awful itchy, dry scalp days.. Methylchloroisothiazolinone and Methylisothiazolinone, also known as the Itchy M’s, are often the very irritating ingredient we overlooked because it wasn’t necessarily a Curly Girl No No like, sulfates, silicones, parabens, synthetic waxes, drying alcohols, and Mineral Oil/ Petroleum.

Just because an ingredient isn’t already on the avoid list for the Curly Girl Method (If you don’t know what to avoid click here)

By learning about this ingredient, you can solve the problem of figuring out which of your products seems to be irritating your scalp, causing dry, itchy, flaky scalps. Never forget my beautiful Queens, healthy hair requires a healthy scalp!

Knowledge of your ingredients is super important so you don’t hinder your hair and scalp health with skin irritating chemicals like Methylchloroisothiazolinone and Methylisothiazolinone. So, let’s get into the most common questions regarding Itchy M’s. Below you will also find the hyperlinks to journal articles to support the data presented in this article.

What are Itchy M’s?

Methylchloroisothiazolinone(MCI ) and Methylisothiazolinone(MI) are preservatives from the family of substances called Isothiozalinones. They are added to cosmetic products to prevent the growth of micro-organisms in the product.

Any product on the market that contains water is predisposed to perishing because of microbial growth such as bacteria, yeast, and fungi, causing issues like discoloration, separation/breakdown of product, and even unpleasant odors. The addition of this preservative extends the shelf-life for in store and consumer storage. 

Methylchloroisothiazolinone and Methylisothiazolinone are normally approved for use in rinse-out cosmetic products and some leave-in styling products.

Why Should I Avoid the Itchy M’s Methylchloroisothiazolinone and Methylisothiazolinone?

If you haven’t experienced anything out of the normal like an increasingly itchy scalp, then you probably haven’t struggled with the use of preservatives. If you have sensitive skin and noticed a major change in your scalp since starting the Curly Girl Method, these two preservatives might be the little buggers give you the trouble.

The Itchy M’s normally give curlies problems for one of two reasons:

  • Sensitive skin
  • The Itchy M was high up on the product label listing

The formulation of products matter! The first five ingredients make up approximately 80% of the product. So if you are having issues with it in one product even though you have no issues with another product that contains the preservatives, it could be the concentration of  preservative within the product.

Methylchloroisothiazolinone and Methylisothiazolinone in high concentrations are known to irritate the skin, and in extreme cases even cause a chemical burn to the skin. 

Dermatologists conducted studies that showed an increase in usage of the preservative by companies since 2009, therefore continuing to increase the consumers sensitivity to the preservatives. The preservative has become so popular within the industry, Methylisothiazolinone was the American Contact Dermatitis Society Contact Allergen of the Year for 2013. ( Rios Scherrer)

In December 2013, the European Personal Care Association, Cosmetic Europe, issued a recommendation for all companies to remove the use of Methylisothiazolinone in leave-in skincare products. Soon after, the Scientific Committee of Consumer Safety (also known as SCCS), also advised the removal of Methylisothiazolinone from leave-in products and Methylchloroisothiazolinone concentrations should be reduced in rinse-off products.

How can I tell if my products contain a large concentration of the Itchy M’s?

The best way to know if you product contains a lot or a little of this preservative is by looking for the placement of the ingredient on labels.

  • Remember first five ingredients of a product equates to approximately 80% of the product.
  • If the preservative is one of the first five ingredients, then the product contains a higher concentration (more) of the preservative.
  • If the at the end of the list on the product label it will make up less than 2% of the product and will therefore have a lower concentration of the preservative.

Let’s look at two product labels for examples. For this example I will be using  the labels of Jane Carter Curls to Go Untangle Me Leave-in and VO5 Herbal Escapes Kiwi Lime Squeeze Conditioner

Jane Carter Curls to Go Untangle Me Leave-In Conditioner is Curly Girl Method Approved. It contains no sulfates, silicones, parabens, drying alcohols, synthetic waxes, or mineral oil/Petroleum. Now while the product is CGM approved, it doesn’t mean it will automatically work for you. As we discussed, if your skin is sensitive you can possibly have an allergic reaction to the product. This leave-in conditioner is a perfect example of low concentrations of Methylisothiazolinone. It is the last ingredient on the list, meaning the product contains the least of this particular ingredient. It can be anywhere  between 0.5% – 2% of the product. More likely than not, you will not experience any issues when using the product. However, over time the product can build up on the hair and scalp if the hair is not properly clarified. So make sure to pay attention to how your hair feels when using a product. This is why I always advise using a minimalist routine, no more than 1-2 styling products. This makes it easier to identify which product is working for you or not working for you.

v05 Herbal Escapes Kiwi Lime Squeeze Conditioner is also Curly Girl Method Friendly, but with many of the drug store products you can easily find, the savings doesn’t always prove to be the right decision. As you can see from the label, Methylchloroisothiazolinone is listed as the seventh ingredient on the label. Since this preservative is listed much higher on the product label, it means there’s a higher concentration of the preservative in the product. Over my few years of research, I’ve noticed many women in the Red Carpet Curls Facebook Group and the Curly Girl Method Support Group International complain of itchy scalp when they switched to the Vo5 conditioners. 99% of the time the problems are almost always the Itchy M’s if the person’s routine hasn’t change.

Make sure to pay attention to your reactions to this ingredient by patch testing the product on a different part of your skin to see how your skin reacts.

If you do experience an allergic reaction, no matter how minor, stop using the product and look for products with natural preservatives or no preservatives at all (will have shorter shelf life)

What else do I need to know about the Itchy M’s?

The Itchy M’s will not cause cancer. They are more of an itchy inconvenience to look out for on labels. It’s the same as having a preference, picking a product that works better for you. The Curly Girl Method is going to be very individualized. No one has the same body chemistry as the person next to them, therefore, we cannot compare our journey to anyone else’s.

Certain season changes can also provoke the Itchy M’s to be even more annoying. Nothing to freak out about, just give your scalp a good scrubbing(don’t use your nails!) and give your strands a bit more moisture, and everything will work out fine.  Apple Cider Vinegar or Lemon Rinses will work to balance out the scalp as well!

I do consider the Itchy M’s to be an ingredient to look out for on labels, so all product lists compiled by Red Carper Curls will include a note if the product contains them or not. Here are the most recent examples.

All the Curly Girl Method Approved Products in Walgreens:

All the Curly Girl Method Approved Products in Sally Beauty:


Pónyai, Györgyi et al. “Methylchloroisothiazolinone/Methylisothiazolinone and Methylisothiazolinone Sensitivity in Hungary.” Dermatology research and practice vol. 2016 (2016): 4579071. doi:10.1155/2016/4579071

Rios Scherrer, Maria Antonietta, and Vanessa Barreto Rocha. “Increasing Trend of Sensitization to Methylchloroisothiazolinone/Methylisothiazolinone (MCI/MI) .” Anais Brasileiros De Dermatologia, vol. 89, no. 3, 2014, pp. 527–528.

The Cosmetic, Toiletry and Perfumery Association.”,

Queen Monroe

Queen Monroe

Curly Girl Method enthusiast and educator. I have been on my own CGM journey for a bit over three years now. I take a scientific approach to the Curly Girl Method. I believe by learning Trichology (the study of hair and scalp) you can better understand your hair's needs and behaviors. This will help when you need to learn ingredients to read product labels. I research and write each and every article in this site. The information used and referenced on this website come from open access, peer-reviewed journal articles from publications such as the Journal of Cosmetic Science and the International Journal of Trichology.

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About Red Carpet Curls

About Adrienne Monroe and Red Carpet Curls : In this section you’ll get to meet your guide…me! I’ll tell you more about my Curly Girl Method Journey along with all the resources you can expect to find on this website. You will also find out exactly what makes Red Carpet Curls different from any other Curly Girl Method Website.

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