Methylisothiazolinone in paint, usually shortened to MI or MIT, is a preservative used to prevent microbial growth during storage.
It’s not just used in paint, but a wide range of water based products, including household cleaners, laundry products and personal care items. MI allergy usually manifests as skin irritation, particularly itching, redness, dryness or dermatitis. Some people also notice eye irritation, headaches or discomfort around freshly painted spaces.
Most standard petrochemical paints contain MI. Some, but not all, natural paints are MI-free, and that can vary by formulation. This is why terms such as natural paint or low VOC paint are not enough on their own to assume a product is free from Methylisothiazolinone.
Let’s take a look at what MI in paint is, why it needs to be included in some natural paints, and how you can identify which natural paints are free from this allergen.
What is Methylisothiazolinone in Paint
Methylisothiazolinone is a preservative. It is a strong biocide commonly added to water based paints to stop bacterial and fungal growth developing in storage.
MI has been identified as a potent allergen. Some people can experience allergic reactions as the paint dries, even if they did not touch it. That’s because as paint dries MI can be released into the air in your home.
Why Mi Causes Allergic Reactions
MI is in a massive array of water based products that need to be kept shelf stable. Cosmetics, shampoos, sunscreen, wet wipes, detergents and many more. That means sensitivity can develop not just from a single product, but from repeated exposure from many sources.
Methylisothiazolinone is now a well recognised sensitiser, and over the past decade there has been a noticeable increase in reported reactions. The most common reaction is contact dermatitis.
What makes this tricky is that reactions don’t always happen immediately. Someone might use a product for years without issue, then suddenly develop sensitivity. Once that happens, exposure to even low levels of the preservative can trigger symptoms.
Further reading: Can you be allergic to paint? | Paint for asthma & allergy sufferers | What is anti allergy paint?
How to Avoid Methylisothiazolinone in Paint
Avoiding MI in paint is less straightforward than it should be. MI is not always obvious from the tin alone. EU labelling rules apply, but paints containing only trace levels may still sit below the threshold for the allergy warning.
Paints described as preservative free are a strong starting point. Mineral, lime, clay and silicate paints are also worth checking, because some of these formulations do not require the same preservation systems as standard emulsions.
It’s important to understand that natural paint or low VOC paint does not automatically mean MI-free. Many standard trade and DIY paints rely on preservatives as part of the formulation, and even within more natural ranges the answer can vary by product and by colour.
MIT / BIT Are Required Preservatives in Some Paints
Water based paints must remain stable, safe and fit for purpose while stored in the tin. Where the pH is not high enough to prevent microbial growth naturally, an approved in-can preservative system is needed.
MIT/BIT falls under the GB biocides rules for Product Type 6 preservatives, which are used to protect products during storage. Natural paint companies may use MIT/BIT because it is effective at very low levels, helping to keep the paint from degrading before it can be used while keeping preservative content as low as possible.
So this means that even a natural paint may still need a trace amount of MIT/BIT if it is not lime based. It is not a case of manufacturers adding it because they want to. In some formulations, they have to include it to keep the paint stable and fit for purpose.
This is why coloured paints such as Auro 555 and Grafclean contain trace MIT/BIT, while white lime based paints such as Ambient Pro do not. Lime paints are naturally highly alkaline, which helps protect the paint from microbial growth without needing the same preservative system.
MIT/BIT may also be present in the liquid pigments themselves. So once a paint is tinted, even a lime paint may contain trace MIT/BIT because the preservative is already in the pigment preparation.
Why Some Paints Don’t Need Mi
Not all paints require preservatives, which is one reason many MI allergy sufferers research using natural paints in their homes. However, although natural paints try to avoid their use, some formulations contain small amounts of the preservative.
Here’s an overview of common paint types that don’t need Mi in the tin.
- Clay Paints - Clay based paints can often be made without preservatives because they are formulated more simply than standard emulsion paints. They rely more on mineral and natural ingredients, so they do not always need the same in-tin protection.
- Lime Paints - Naturally high alkalinity creates an environment where bacteria, mould and yeasts struggle to survive, so preservatives like MI are not needed in the same way. This is one of the reasons lime based paints remain such a useful option in traditional buildings.
- Silicate Paints - Silicate paints also avoid the chemical based preservation model. They are highly breathable, mineral based and alkaline, and their chemistry is very different from a standard acrylic emulsion. That means they can offer a durable finish without depending on the same preservative systems.
Coloured Natural Paints
It’s always white base paints that are Mi free - the addition of coloured pigments will introduce small amounts of Mi into the paint formulation.
Nevertheless clay, lime and silicate paints are often the strongest place to start if you are trying to avoid Methylisothiazolinone. Just don’t plan on adding tints if you’re highly sensitive.
Mi-Free Paint Options
If you are trying to avoid Methylisothiazolinone completely, here’s some examples of paints that do not contain Mi.
AURO Clay Paint 331 - A modern clay paint that is free from preservatives and rated as very low emission under the AgBB scheme. With an sd value below 0.015 m, it is extremely breathable and well suited to sensitive indoor environments where air quality is a priority.
AURO Lime Paint 344 - Traditional mineral lime paint with a naturally high pH. This type of formulation does not require preservatives at all and creates a breathable, matt finish with a classic lime character that develops over time.
AURO Silicate Paint 303 - A more durable option that still avoids preservatives. It offers excellent breathability (sd value below 0.01 m) alongside improved washability, making it a practical choice for modern interiors where a balance of performance and air quality is needed.
Graphenstone Ambient Pro - Not only MI free but offering your home natural air purification properties. It’s the top end option within the Graphenstone ranges and is a fabulous natural interior emulsion paint. Highly breathable (Sd value below 0.14).
If you want to explore further options, you can view the full range of our MI-free paints here.
Choosing Paint More Carefully
If you are trying to avoid Mi, choosing paint more carefully means you need a good understanding about what is actually in the tin you’re going to apply in your home.
Terms such as eco, natural, or low VOC aren’t a green light on their own. Make sure you familiarise yourself with the TDS, or speak to us about your needs. Our team of paint experts have great knowledge about Mi in paints, and will be delighted to help. Contact Us for assistance.
