Know Your Ingredients: Methylchloroisothiazolinone

by Gio


What it is
Methylchloroisothiazolinone belongs to a group of compounds called Isothiazolinones.

What it does
Methylchloroisothiazolinone is a preservative: it protects products from the growth of fungi, bacteria and yeast, thus prolonging their shelf life.

Side effects
Methylchloroisothiazolinone is an irritant and a strong allergen. Because of that, it is mostly used, in small concentrations, in rinse-off products so the chances of it causing negative reactions are much smaller.

(Source: Contact Dermatitis, November 2011)

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Trisha May 8, 2010 - 8:38 pm

Why kinds of things would you find this in?
.-= Trisha´s last blog ..Ultimate Beauty Day 4: Try Something New Today =-.

beautifulwithbrains May 9, 2010 - 7:12 pm

Trisha, this preservative can be found pretty much in all kind of products: makeup, skincare, shampoos, bath products and suntan products.

Sheri December 28, 2010 - 4:18 am

I’m searching for beauty products that DO NOT contain Isothiazolinones and having a difficult time. Do you know of any websights that would list such products?

beautifulwithbrains December 28, 2010 - 4:52 pm

Sheri, unfortunately I don’t know such websites but I know that some online retailers like and list the ingredients of most of the products they sell. You can just search for a product you’re interested in buying on there and see if it contains Isothiazolinones. I’m sorry I couldn’t be of more help.

Carole winter April 23, 2014 - 3:22 pm

Sheri,I had the North American patch test though a dermatologist and tested positive to it.If you can obtain the test it will tell you many products to avoid. Hair products /dyes ,paint,pet care,yard care. You won’t believe the hair and cosmetic products that contain it. I switched to Aussie hair shampoo and conditioner, ivory soap,all detergent.Hope this helps, if you are allergic this substance can wreak havoc to your skin and system.

Rebekah Baharestan January 22, 2016 - 11:31 pm

there’s lists of products which contain Methylisothiazolinone as well as things that are known to contain the other isothiazolinones in the “Household product database” for cleaners such as dishsoaps and laundry detergent liquids, car care, floor care, room sprays furniture polishes etc. Do have a look at EWG “healthy guide to cleaning” and have a look at “skindeep’ app also by EWG (Environmental Working Group) for cosmetics ( put in your chemical and see what pops up, or look at ratings and stay in the green zone of 2 and under or A ratings. Also- go on facebook and look up “Allergy to Isothiazolinone, Methylisothiazolinone and Benzisothiazolinone ” to see reaction pictures, ongoing threads of comments, photos of products both free from these pesticide/biocide preservatives as well as those that contain them.

Gio January 27, 2016 - 9:14 am

Rebekha, thank you for your comment. I think, if you want to avoid a particular ingredient, the EWG database can help, as it’ll tell you exactly which products contain it. But, when it comes to the safety of cosmetic ingredients, the EWG simply isn’t a reliable source. This article explains why, check it out:


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