What is Methylisothiazolinone (MI) & Benzisothiazolinone (BI) and why are they used?

What is Methylisothiazolinone (MI) & Benzisothiazolinone (BI) and why are they used?

What is Methylisothiazolinone & Benzisothiazolinone?

Methylisothiazolinone & Benzisothiazolinone are preservatives that are widely used in cosmetic, household, and industrial products to prevent gram + and gram – bacteria, molds, and yeast in products around the world.  They are approved for use in “rinse-off” products in Canada, Europe, and the USA.

Why do we use Methylisothiazolinone & Benzisothiazolinone?

Rustic Strength uses the most effective preservatives on the market to protect the end user from bacteria, mold, yeast, and fungus.  

We use this preservative at the smallest amount that we can, while still being effective (less than .1%) and it is only used in our rinse-off formulations.  

When cleaning with our laundry detergent or liquid dish soap, water is added to the base product.  This water dilutes the concentration even more and washes away from the clothing and from your hands when scrubbing dishes. According to a study done in 2018, by the National Library of Medicine,

…MI could not be detected in any specimen of clothes washed under household conditions. The detection limit was 0.5 ppm.” 

What is the benefit of using Methylisothiazolinone & Benzisothiazolinone

We use these preservatives because they are the best at controlling microbial growth (bacteria, fungus, algae, mold) and spoilage.  Each time you open the bottles and expose the product to air or transfer it to another bottle, it increases the potential for microbes and spoilage.  This is not just our products; it goes for any product you are transferring from bottle to bottle.  By using one of the most effective preservatives on the market we are protecting the end user from harm.

Is Methylisothiazolinone & Benzisothiazolinone safe to use? Is it non-toxic?

These two preservatives are safe to use in rinse-off products and have been approved by the EPA, FDA, Europe, and Canada.  There are government guidelines for usage rates for these chemicals.

This all being said, if you search these two materials you will find a lot of articles telling you how dangerous these two chemicals are.  We know it is scary when you research ingredients on the world wide web.  If you read carefully, they are for leave-on products, not rinse-off products.  Using these two preservatives with leave-on products like lotions, cosmetics, and lip balms could cause contact dermatitis in some individuals. A lot of the studies and chemical information that you read about are done on animals at higher than allowed percentages to determine safety for humans and the environment. 

Methylisothiazolinone and Benzisothiazolinone are biodegradable, not formaldehyde, not cancer-causing, and have been listed by the EPA as a CleanGredient.  


In Summary

Our mission is to always have safe, effective, and eco-friendly products.  We keep in mind the end-user when choosing our ingredients.  This is why we chose the most effective combination of preservatives and use it at the least amount possible in our products. We research all ingredients and make decisions based on scientific proof.  

We invite you to do your own research! 

Scientific journals and articles are the foundation of evidence-based decisions at Rustic Strength. Blogs can provide helpful information. However, if it can not cite scientific articles, its claims stand on little. 

Bacteria - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5755462/
National Library of Medicine - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5755462/
Rinse-off products - https://journals.sagepub.com/doi/10.1177/10915818211015795
Europe and Canada - https://chemistscorner.com/discontinuing-a-preservative/
Leave-on products - https://cen.acs.org/articles/94/i16/Preservative-leavecosmetics-banned-EU.html

Other helpful sources


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