Preservatives in Natural Products: Methylisothiazolinone and Methylchloroisothiazolinone


(As of 6/6/2015)

The primary focus of Nature’s Pulchritude is to educate. This post is the second in a series of in depth posts that will educate you about the various preservatives in hair and skin products, as well as their potential toxicity.

Preservatives are added to cosmetics, personal care products, and food to maintain a products integrity and stability by inhibiting or reducing the growth of microorganisms such as bacteria and fungus (FDA). Most products sold via retail sit for extended periods of time during shipping, in a warehouse, and on store shelfs that allow enough time for a product to spoil or cause microbial growth which render the product unfit for use. This is particularly true for products that contain water, such as many conditioners and moisturizers, and other active ingredients (antioxidants and emulsifiers) that would otherwise lose their effectiveness and stability over time.

Preservatives are chosen in cosmetics based on a variety of factors which include ability to inhibit growth over a broad spectrum and method of derivation (natural vs. synthetic). Preservatives tend to be in concentrations less than 2% of the weight of the formula, however, widespread use of potentially harmful preservatives, such as parabens, has been a great cause of concern for some scientists and consumers. The Food, Drug, and Cosmetic Act does not grant the Food & Drug Administration the authority to regulate the use of preservatives unless it is known to be “poisonous or deleterious” (FDA).


Isothiazolinone is a heterocyclic (‘ring’ containing more that 1 element) chemical compound of which its derivatives are typically used as antimicrobial agents and biocides in a variety of personal care products including hair conditioners, shampoos, foundations, eyeliners, mascaras, lotions, and soaps.  The most commonly used isothiazolinone group preservatives are Methylisothiazolinone and Methylchloroisothiazolinone, which have been in use since the 1970’s.  Methylisothiazolinone (MIT) has an ethane (CH3) molecule attached to a Nitrogen (N) atom, whereas Methylchloroisothiazolinone (MCI) has a Chlorine (Cl) atom attached to the ring in addition to the ethane molecule.  Use of MIT and MCI have increased in recent years, perhaps in part to the decline in paraben use, which has resulted in an increase of reported sensitization incidences caused by using products containing these two preservatives.  Allergic contact dermatitis is a common indicator of sensitization from MIT and MCI, which is an immunotoxic response that can cause rashes or skin lesions.  Allergic contact dermatitis has been observed as a result of sensitization to MIT and MCI since the late 1980s.

Methylisothiazolinone Chemical Structure
Methylchloroisothiazolinone Chemical Structure


Methylisothiazolinone (MIT) and Methylchloroisothiazolinone (MCI) are often used in conjunction as preservatives.  A 2010 study found that MIT/MCI were present in 23% of 204 tested products (92 shampoos, 61 conditioners, 34 liquid soaps, and 17 wet tissues) (Yazar et al. 2010).  Despite MCI/MIT being allowed in personal care products up to 0.00075% (leave-on) or 0.0015% (rinse off) in the United States, there has been a significant incidence of allergic contact dermatitis from sensitization from these products (Yazar et al. 2010; Castanedo-Tardana and Zug 2013).  The frequency of an MIT allergy is approximately 1.5% in Europe, 3.5%-6.5% in an Australian study (tested 653 patients); the rate is unknown in the United States (Castanedo-Tardana and Zug 2013; Boyapati et al. 2013).  It is very interesting and troubling to know that a preservative at a very low concentration (7.5-15 parts per million) can yield such an allergic response, to the extent that it was named Contact Allergen of the Year by the American Contact Dermatitis Society in 2013 (Castanedo-Tardana and Zug 2013).  This is a prime example that certain ingredients being in low concentration does not always equate their safety, particularly when they are present in products that are used multiple times a day, therefore a continuous low exposure (Yazar et al. 2010).  Once skin has become sensitized, it will continuously react to exposure despite the dosage.  MIT and MCI are often used in conjunction with a variety of other preservatives and skin penetration enhancers that may potentially increase the risk of an allergic reaction.  In fact, last weeks Label Poise product was a lotion that contains four different preservatives (methylparaben, phenoxyethanol, propylparaben, and methyisothiazolinone).  MIT has been shown to be neurotoxic in ‘in vitro’ tests of neurons in rat brain tissue cultures; similar studies using MCI showed that it was 30-100 times more effective of causing a neurotoxic response.  Methyisothiazolinone is also a known environmental toxin, particularly to fish, though the majority of incidences are cause by non-cosmetic uses.


Methyisothiazolinone and Methylchloroisothiazolinone are both known skin allergens and sensitizers that are used in approximately 23% of personal care products, though they typically are not found in products marketed as natural or organic.  Whether or not you choose to use products containing these preservatives is entirely up to user discretion. If you have used products containing MIT and MCI, and noticed a skin reaction you should discontinue use.  Otherwise, they should not be a significant cause of concern.



Boyapati, A., Tam, M., Tate, B., Lee, A., Palmer, A., and R. Nixon. 2013. “Allergic contact dermatitis to methylisothiazolinone: Exposure from baby wipes causing hand dermatitis.”  Australasian Journal of Dermatology. 54(4):254-267.

Castanedo-Tardana, M. and K. Zug.  2013.  Methylisothiazolinone.  Dermatitis.  24(1): 2-6.

Yazar, K., Johnsson, S., Lind, M., Boman, A., and C. Liden. 2010. “Preservatives and fragrance in selected consumer-available cosmetics and detergents.”  Contact Dermatitis.  64: 265-272.

11 thoughts on “Preservatives in Natural Products: Methylisothiazolinone and Methylchloroisothiazolinone”

  1. What do you know about borax in lotion? I use an awesome product from Simply Organic Botanicals (How Now Brown Cacao), and the only questionable ingredient is the borax. What are your thoughts?

    1. Borax is natural, it is mined as Sodium Borate. It can be a slight skin irritant in pure form as it is alkaline. It is liked used as an emulsifier as beeswax alone will not keep it emulsified over time. It is generally not toxic and does not absorb through the skin. The product you use has it as the second to last ingredient so it should be fine, though there one account that said the more you use products with borax the more you will need to use lotion.

  2. You should probably update this article, please. There is growing concern for the cumulative effects of exposure to MI and it is not actually as safe as originally thought. And, it’s replaced parabens in a lot of organic products. This 2014 report (see bottom of p.27) should raise a red flag

    In the UK, allergic reactions are now occurring in the population at a rate of 6% (some studies estimate as high as 10% of the population has been sensitized).

    1. Yes . Exactly. It is also mentioned in the preservative section ; thiazolinines: that they are not commonly found in natural or organic products. This is NO LONGER TRUE. Only certified USDA organic products . “natural products ”
      Or products claiming to be environmentally friendly and natural are misleading the public consumers.

  3. Please re review current EU sccs literature and ammended saftey assesments for methylisothiazolinone / it is of VERY high CONCERN. Your website is very informative and I really like your research but you must update and edit the section on Thiazolinines as preservatives- it is out of date/ not current, and incorrect regarding current safety assesments as well as misleading in my opinion.

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