Isothiazolinones are preservatives widely used in many industrial sectors, including cosmetics , paints, cleaning products, and water treatment. Their antimicrobial efficacy makes them indispensable preservatives, but their use also raises concerns due to their allergenic and toxic potential. This article offers a comprehensive exploration of these compounds, from their chemical structure and regulation to laboratory analysis methods and alternative solutions.
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1. Introduction
A family of indispensable conservatives
Isothiazolinones are organic compounds belonging to the thiazolinone family, characterized by the presence of a ring containing both a sulfur atom and a nitrogen atom. They possess powerful antimicrobial properties, making them particularly valued preservatives in the cosmetics, food, and chemical industries.
One of the main advantages of isothiazolinones is their ability to inhibit the growth of bacteria, yeasts, and molds, even at very low concentrations. This property makes them particularly effective in water-based formulations, where the risk of microbial contamination is high. However, due to their potential to cause irritation and sensitization, their use is subject to strict regulations.
A history marked by regulatory changes
The introduction of isothiazolinones into industrial formulations dates back to the 1970s, when manufacturers were looking for more effective alternatives to parabens and formaldehyde. Initially used in a wide variety of products, their use was gradually restricted after their allergenic effects were demonstrated, particularly in cosmetics and hygiene products.
In 2015, the European Union banned the use of certain derivatives, such as methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI), in leave-on cosmetics. Since then, regulations have continued to evolve to limit their concentration and regulate their use in other industrial applications.
Issues and controversies surrounding isothiazolinones
Isothiazolinones are at the heart of a debate concerning their effectiveness as preservatives and their potential impact on human health. On one side, manufacturers emphasize their essential role in ensuring the microbiological safety of products. On the other, dermatologists and regulatory bodies warn of the increased risk of contact dermatitis, particularly in sensitized individuals.
This paradox raises several essential questions:
- What are the most commonly used derivatives and what are their specific characteristics?
- What are the health risks associated with exposure to isothiazolinones?
- What alternatives are available to replace these preservatives?
- How do laboratories analyze the presence of these compounds in products?
These questions will be explored in detail in this article, in order to provide a complete overview of the role and implications of isothiazolinones in modern industries.
2. What is isothiazolinone?
Chemical structure and classification
Isothiazolinones belong to the family of sulfur-nitrogen heterocycles. Their basic structure is based on an isothiazolinone , a five-membered ring containing both a nitrogen and a sulfur atom. This configuration gives them powerful biocidal properties , enabling them to inhibit the growth of bacteria, yeasts, and molds in many industrial formulations.
Isothiazolinones are generally used in mixtures with other preservatives, which optimizes their effectiveness while minimizing their concentration. Their mechanism of action relies on their ability to denature microbial proteins , thereby causing the death of microorganisms.
The main isothiazolinone derivatives used in industry include:
- Methylisothiazolinone (MI) : frequently used in cosmetics and cleaning products.
- Methylchloroisothiazolinone (MCI) : often combined with MI to increase its antimicrobial efficacy.
- Benzisothiazolinone (BIT) : used mainly in paints, adhesives and industrial fluids.
- Octylisothiazolinone (OIT) : integrated into wood coatings and treatments due to its enhanced antifungal action.
Physicochemical properties
Isothiazolinones share several physicochemical characteristics that influence their stability and effectiveness as preservatives. Among their main properties are:
- Solubility : They are generally soluble in water and organic solvents , which facilitates their incorporation into various formulations.
- Thermal stability : some isothiazolinones, such as MI and BIT, retain their antimicrobial activity even at high temperatures .
- Degradability : Although their biodegradability varies according to their chemical structure, some isothiazolinones can persist in the environment , posing challenges in industrial waste management.
Main derivatives and specific features
Methylisothiazolinone (MI) and methylchloroisothiazolinone (MCI)
MI and MCI are among the most widely used isothiazolinones, particularly in cosmetics, detergents, and paints . Their effectiveness stems from their strong antimicrobial action , which prevents bacterial growth in water-based products. However, their allergenic potential has led to a reduction in their use in leave-on cosmetics since 2015.
Benzisothiazolinone (BIT)
BIT is primarily used in paints , adhesives, inks, and varnishes due to its resistance to extreme conditions (temperature, pH). Unlike MI and MCI, it is less skin-sensitizing, making it an attractive alternative for certain industrial applications.
Octylisothiazolinone (OIT)
OIT is used for its antifungal action in coatings , wood preservatives, and exterior paints . Its chemical structure makes it more stable in environments exposed to humidity and temperature variations.
Isothiazolinones are therefore a family of preservatives essential for many industrial sectors, but their use must be controlled due to their potentially irritating and sensitizing effects. The regulations governing their use will be discussed in the following section.
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3. Applications of isothiazolinones
Cosmetics industry: a controversial preservative
Isothiazolinones are widely used in the cosmetics industry for their antimicrobial properties . They help prevent the growth of bacteria and mold in aqueous products such as shampoos, lotions, shower gels, and moisturizers .
Until 2015, methylisothiazolinone (MI) and methylchloroisothiazolinone (MCI) were present in many cosmetics, including leave-on products. However, due to the high risk of contact dermatitis , the European Union banned their use in leave-on products (Regulation (EC) No 1223/2009). Today, they are still permitted in rinse-off products , but at a maximum concentration of 15 ppm for the MI/MCI mixture and 100 ppm for MI alone.
Main applications in cosmetics:
- Hair products (shampoos, conditioners)
- Skin care products (shower gels, moisturizing creams)
- Makeup and cleansing wipes
- Baby care products (subject to certain restrictions)
Food industry: a limited preservative
Unlike parabens or organic acids, isothiazolinones are not commonly used as food preservatives due to their allergenic potential . However, they can be present indirectly in the food industry , particularly in food processing equipment and packaging .
The main risk is the migration of isothiazolinones from packaging into food , which is strictly regulated by EC Regulation No. 1935/2004 . Migration tests are essential to ensure that these substances do not contaminate food.
Possible uses in the agri-food sector:
- Disinfectants for industrial equipment
- Antimicrobial agents in plastic packaging and food films
- Cleaning products that come into contact with food surfaces
Water treatment and paints: a massive use
Isothiazolinones are commonly used in industrial water treatment and paint formulation due to their broad spectrum of action against microorganisms .
Water treatment
In cooling circuits and cooling towers, the presence of bacteria and algae can lead to deposits and a decrease in system efficiency. Isothiazolinones are then used to inhibit microbial growth , particularly in:
- Air conditioning systems
- Industrial water tanks
- Energy production facilities
However, their environmental impact is a source of concern, particularly due to their aquatic toxicity . Numerous regulations, such as the European REACH , impose strict limits on their concentration in industrial discharges.
Paints and coatings
In paints and varnishes, isothiazolinones prevent the growth of mold and bacteria , thus extending the lifespan of the products. They are found in particular in:
- Water-based paints used in construction
- Industrial coatings exposed to moisture
- Glues and inks
Among the most used derivatives, benzisothiazolinone (BIT) and octylisothiazolinone (OIT) are preferred for their increased stability and prolonged effectiveness.
Other sectors: household products, glues and inks
Isothiazolinones are also present in various everyday products , where they play an essential role in preserving aqueous formulations:
- Household products : multi-purpose cleaners, disinfectants, fabric softeners
- Glues and adhesives : preventing bacterial growth in water-based glues
- Inks and varnishes : improving the preservation of water-based products
Although these uses help ensure the microbiological safety of products , they also pose problems of allergies and environmental toxicity , requiring increased monitoring and suitable alternatives.
In the next section, we will look at the toxicity problems and regulations governing the use of isothiazolinones.
4. Toxicity issues and regulations
Effects on human health
Isothiazolinones are known for their antimicrobial efficacy , but they also pose risks to human health , particularly due to their allergenic potential and skin toxicity . Several studies have demonstrated that these preservatives can cause severe skin reactions , especially in sensitized individuals.
Contact dermatitis and allergies
One of the main problems associated with isothiazolinones is their ability to trigger allergic skin reactions . These reactions manifest as redness, itching, eczema, and inflammation .
The conservatives most affected are:
- Methylisothiazolinone (MI) : common cause of allergic dermatitis, particularly in cosmetics.
- Methylchloroisothiazolinone (MCI) : even more irritating when combined with MI.
- Benzisothiazolinone (BIT) : although less common, it can cause irritation in sensitive individuals.
In 2013, a study conducted by the British Association of Dermatologists revealed that 10% of patients suffering from contact dermatitis were sensitized to MI . Faced with this situation, the European Union decided to restrict its use in cosmetics .
Systemic toxicity and inhalation
In addition to skin allergies, some studies suggest that inhaling vapors or aerosols containing isothiazolinones could cause respiratory irritation and inflammatory lung reactions . This particularly concerns spray paints, aerosol cleaning products, and cosmetic mist sprays .
In animals, acute toxicity tests have shown that high doses of isothiazolinones can cause neurological effects , but these results remain to be confirmed in humans.
Regulations and restrictions
Because of these risks, several international regulations have progressively limited or prohibited the use of isothiazolinones in certain products .
European (EU) standards
The European Union has imposed several restrictions on the use of isothiazolinones, particularly in cosmetics and consumer products. These rules are established by Regulation (EC) No 1223/2009 , which sets the following limits:
- MI and MCI have been banned in leave-on cosmetics since 2015.
- Maximum concentration of 15 ppm (parts per million) for the MI/MCI mixture in rinse-off cosmetics (e.g. shampoos, shower gels).
- Maximum concentration of 100 ppm for MI alone in rinse-off cosmetics.
In parallel, the REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) imposes restrictions on the use of isothiazolinones in paints, adhesives and industrial biocides, in order to limit the exposure of workers and consumers .
Regulations in the United States and Asia
In the United States, the FDA (Food and Drug Administration) authorizes the use of isothiazolinones in cosmetics, but with restrictions similar to those in the European Union . The EPA (Environmental Protection Agency) regulates their use in industrial products and water treatment.
In Asia, several countries such as Japan and South Korea have implemented strict regulations to limit the concentration of isothiazolinones in cosmetics. China also imposes restrictions through its Cosmetics Regulatory Authority (CSAR) .
Prohibitions and regulated alternatives
Some isothiazolinones, such as the MI/MCI mixture , have been banned in certain products but remain permitted under certain conditions in other industrial sectors. Manufacturers must therefore:
- Respect the maximum concentrations permitted according to the regulations in force.
- Conduct safety tests and toxicological studies to assess risks.
- Explore less sensitizing alternatives , such as natural preservatives or other better-tolerated synthetic biocides.
Regulations surrounding isothiazolinones are constantly evolving, driven by new scientific studies and health concerns. Laboratory analysis is essential . The next section will detail the various analytical techniques used to detect and quantify isothiazolinones in consumer products and industrial formulations.
5. Detection and analysis of isothiazolinones in the laboratory
Isothiazolinone analysis is essential to ensure regulatory compliance , consumer safety , and prevent contamination risks in various industrial and consumer products. Laboratories use advanced techniques to detect and quantify these preservatives, relying on standardized and accredited methods .
Analytical techniques used
Several analytical methods are commonly used to detect and measure the concentration of isothiazolinones in cosmetics, paints, household products and industrial waters .
High-performance liquid chromatography (HPLC)
chromatography (HPLC) is one of the reference methods for the analysis of isothiazolinones. It allows for the separation, identification, and quantification of these preservatives with high precision.
- Principle : The sample is injected into a chromatographic column where the compounds are separated according to their affinity with the mobile phase and the stationary phase.
- Advantages : Very precise, fast and suitable for complex matrices (cosmetics, paints, industrial waters).
- Limitations : Requires specialized equipment and sample preparation.
UV-Vis spectroscopy
UV-Vis spectroscopy is an analytical method used to detect isothiazolinones by measuring their absorption of ultraviolet light .
- Principle : Isothiazolinones absorb light at a specific wavelength, which allows their concentration to be estimated.
- Advantages : Fast and simple method, suitable for routine analyses.
- Limitations : Less specific than HPLC and less effective for complex samples.
Gas chromatography-mass spectrometry (GC-MS)
Gas chromatography-mass spectrometry (GC-MS) is used to detect traces of isothiazolinones in complex matrices, such as cosmetics and industrial waters.
- Principle : After chromatographic separation, the isothiazolinones are ionized, then analyzed according to their mass/charge ratio.
- Advantages : Very sensitive, capable of detecting minute concentrations.
- Limitations : High cost and need for advanced expertise.
Immunochemical methods (ELISA)
ELISA (Enzyme-Linked Immunosorbent Assay) tests allow for rapid detection of isothiazolinones in finished products.
- Principle : Based on an antigen-antibody reaction specific to isothiazolinones.
- Advantages : Fast and suitable for quality control in companies.
- Limitations : Less precise than chromatographic methods.
Regulatory compliance and accreditations
To comply with regulations, isothiazolinone analyses must be carried out in accredited laboratories according to strict standards, such as:
- ISO 17025 : International standard guaranteeing the reliability and traceability of analyses.
- COFRAC : French accreditation ensuring compliance with regulatory requirements .
- REACH and EC Regulation No. 1223/2009 : Impose maximum thresholds and mandatory testing in certain products.
The importance of testing for manufacturers
Laboratory analyses are crucial for companies wishing to:
- Verify the regulatory compliance of their products before placing them on the market.
- Evaluate the stability of formulations containing isothiazolinones.
- Ensure the absence of cross-contamination in production lines.
- Prevent risks to consumers and reduce product recalls.
Specialized laboratories, such as those in the YesWeLab , offer analytical services tailored to the needs of manufacturers , guaranteeing reliable and usable results to ensure the safety and compliance of products containing isothiazolinones.
6. The importance of laboratory compliance testing with YesWeLab
YesWeLab, through its network of over 200 partner laboratories , offers advanced analytical services to detect and quantify isothiazolinones in a wide range of products.
Specific analyses for the cosmetics and food industries
YesWeLab offers tests tailored to the requirements of cosmetics and food packaging . These analyses include:
- Detection and quantification of isothiazolinones by HPLC and mass spectrometry .
- Assessment of the allergic risks associated with the presence of these preservatives.
- Testing of formulations before placing them on the market.
Migration tests for food and cosmetic packaging
Packaging materials containing isothiazolinones can migrate into food or cosmetic products , posing a risk to consumers. YesWeLab conducts global and specific migration tests in accordance with European and American (FDA) regulations.
Detection of isothiazolinones in industrial water and paints
Isothiazolinones are widely used in water treatment and industrial coatings . YesWeLab offers analyses that allow you to:
- Monitor the presence of isothiazolinones in wastewater and cooling systems.
- Quantify their concentration in industrial paints and coatings to ensure compliance with REACH regulations.
- Check for the absence of cross-contamination at production sites.
Personalized support for manufacturers
In addition to providing accurate and reliable analyses, YesWeLab supports its clients with:
- A regulatory consulting service to ensure the compliance of formulations.
- Personalized follow-up with experts to analyze the results and propose tailored solutions.
- A digital platform allowing manufacturers to centralize their analysis orders, track their samples and view results in real time .
Thanks to YesWeLab's expertise, manufacturers have a trusted partner to ensure the safety, compliance and quality of their products containing isothiazolinones.
In the following section, we will explore alternatives to isothiazolinones and possible solutions to reduce their impact on health and the environment.
7. Alternatives to isothiazolinones: what solutions?
Faced with growing concerns about the allergenic and toxic effects of isothiazolinones, many industries are seeking alternative solutions to preserve their products without compromising consumer safety. The goal is to find effective substitutes that comply with regulations and are environmentally friendly.
Less aggressive natural and synthetic preservatives
Several alternatives to isothiazolinones are currently being explored, particularly in the cosmetics, paints, packaging and household products .
Organic acids and their salts
Organic acids are increasingly used as preservatives due to their safer toxicological profile and antimicrobial efficacy . Commonly adopted solutions include:
- Sorbic acid and potassium sorbate : effective against yeasts and molds, these preservatives are widely used in food and cosmetic products.
- Benzoic acid and sodium benzoate : used mainly in the food industry, they are also used in some cosmetic and pharmaceutical formulations.
- Dehydroacetic acid : a synthetic preservative often incorporated into cosmetic formulations as an alternative to isothiazolinones.
Essential oils and plant extracts
Essential oils possess natural antibacterial and antifungal properties , making them potential preservatives in certain formulations:
- Tea tree essential oil : effective against a broad spectrum of bacteria and fungi.
- Grapefruit seed extract : used in cosmetics and personal care products due to its antimicrobial action.
- Rosemary and oregano essential oils : known for their preservative effects in natural formulations.
While these alternatives are promising, their effectiveness depends on the concentration and pH of the final product . They sometimes require combination with other antimicrobial agents to ensure complete protection.
Innovations and new molecules tested in the laboratory
Researchers are working on developing new preservative molecules with a low allergenic risk and minimal environmental impact . Among the solutions currently being studied are:
- Antimicrobial peptides : some natural peptides, derived from microorganisms or plants, show an ability to inhibit bacterial growth without irritating effects on the skin.
- Antimicrobial polymers : these innovative materials slow down microbial growth by gradually releasing preservatives, thus reducing the need to add large quantities of synthetic preservatives.
- Nanotechnologies : silver or copper nanoparticles are being studied for their biocidal efficacy , although their environmental impact is still the subject of in-depth research.
Strategies to reduce the use of preservatives
In addition to replacing isothiazolinones, certain strategies can reduce the need to add preservatives by optimizing formulation and manufacturing processes :
- Smart packaging : some packaging incorporates antimicrobial agents that limit the proliferation of microorganisms without requiring the addition of chemical preservatives.
- Advanced sterilization techniques : irradiation, cold pasteurization and the use of ultraviolet filters extend the shelf life of products without harsh preservatives.
- pH adjusted and optimized formulation : modifying the pH of products to create an environment hostile to bacteria can reduce reliance on synthetic preservatives.
Towards a gradual transition
Adopting alternatives to isothiazolinones doesn't happen instantly. Manufacturers must:
- Testing the effectiveness of new preservatives in their formulations.
- Ensure the regulatory compliance of the chosen alternatives.
- Evaluate the stability and shelf life of products with these new antimicrobial agents.
Specialized laboratories, such as those in the YesWeLab , play a key role in this transition by carrying out preservation tests , stability studies and regulatory analyses on the new solutions developed.
8. Conclusion
Isothiazolinones play a vital role as preservatives in many industrial sectors, including cosmetics, paints, household products, and water treatment . Their antimicrobial properties prevent the growth of bacteria, yeasts, and molds, thus ensuring the stability of formulations and consumer safety .
However, their use raises major health and environmental concerns . Numerous studies have shown that certain isothiazolinones, such as methylisothiazolinone (MI) and methylchloroisothiazolinone (MCI) , are responsible for severe allergic reactions , including contact dermatitis. Faced with these risks, authorities have progressively restricted their use, imposing strict concentration limits and prohibiting certain uses in cosmetics and food packaging .
In this context, laboratory analysis of isothiazolinones has become an essential step for manufacturers wishing to:
- Comply with current regulations (EC Regulation No. 1223/2009, REACH, ISO 17025, COFRAC).
- To ensure the conformity of their products before they are placed on the market.
- Avoid product recalls and penalties related to excessive concentrations of these preservatives.
The importance of laboratory analysis with YesWeLab
Thanks to its network of specialized partner laboratories , YesWeLab supports companies in the analysis of isothiazolinones by offering:
- Detection and quantification tests (HPLC, mass spectrometry, UV-Vis spectroscopy).
- Migration analyses for food and cosmetic packaging.
- Regulatory and scientific support to optimize product compliance.
In parallel, evolving standards are encouraging the adoption of alternative solutions to limit or replace isothiazolinones. Natural preservatives, antimicrobial peptides, and new formulation strategies are paving the way for safer alternatives that are better for consumer health.
A balance between efficiency and safety
Manufacturers today must find a balance between the effectiveness of preservatives and the safety of formulations . The challenge is to minimize the risks of exposure while guaranteeing the shelf life and quality of products .
YesWeLab 's expertise enables companies to meet these challenges by conducting precise tests that comply with international standards and are tailored to the requirements of different industrial sectors. By anticipating regulatory changes and investing in innovative alternatives , manufacturers can ensure safer and more responsible production .
