Methylisothiazolinone: A preservative that is bad for your hair and skin

Preservatives in cosmetics

There are many different types of preservatives used in cosmetics.

If cosmetics spoil or deteriorate, they can have serious adverse effects on the skin and body, which is why most cosmetics contain preservatives.

However, along with fragrances and synthetic colorants, preservatives in cosmetics are more likely to cause skin problems. Methylisothiazolinone, which is introduced in this article, is one of them.

Methylisothiazolinone, commonly used in shampoos

In places with a lot of water and moisture, bacteria proliferate. For this reason, products that are often used in the bathroom, such as hand soap, shampoo, and body soap, require stronger antiseptic and antibacterial properties.

In the past, a preservative called triclosan was commonly used, but in 2016, soaps and body washes containing triclosan were banned in the United States because its safety had not been established.

Following this trend, the Japanese government also encouraged a switch in ingredients.
As a result, the use of triclosan has decreased and instead the use of isothiazolinone preservatives has increased.

Is methylisothiazolinone safe?

Triclosan has been banned due to its unclear safety. So is methylisothiazolinone, which has been increasingly used instead, safe?

In fact, there is data that suggests this is not the case.

Another compound in the methylisothiazolinone family is methylchloroisothiazolinone .

These two are effective preservatives with strong antibacterial properties even at low concentrations, and are often combined in mixed ingredients.

However, it is known to cause skin sensitization and irritation, and also has endocrine disrupting effects .

It has also been shown to be highly toxic to aquatic organisms as well as humans.
From these findings, it seems likely that it may be just as toxic as the banned triclosan.

Effects on skin and health

Both methylisothiazolinone and methylchloroisothiazolinone have been shown to be irritating and sensitizing to the skin, and are known to cause contact skin allergies .

Between 2009 and 2015, contact allergies caused by these preservative ingredients increased worldwide .
As a result, the EU banned the simultaneous use of these two ingredients in leave-on products (cosmetics that are not washed off immediately after use) in 2016.
In 2017, methylisothiazolinone alone was also banned from use in leave-on products.

In addition to its effects on the skin, it has also been suggested that it may be associated with cytotoxicity, neurotoxicity, and carcinogenicity.
There are also concerns about the endocrine disrupting properties of methylisothiazolinone.

In Japan, up to 0.01% is permitted.

Methylisothiazolinone is banned in leave-on products in the EU, but in Japan it can be used up to 0.01%.

Additionally, even in rinse-off products such as shampoo, whereas Japan allows for up to 0.01% content, the EU prohibits the use of more than 0.0015%.

Allergic reactions to isothiazolinone preservatives have been reported at concentrations ranging from 0.00075% to 0.01%.
For this reason, it may not be possible to say with certainty that the regulated amount in Japan is safe.

People with sensitive skin, allergies, or atopic skin should avoid it as much as possible.