Are Linseed & Tung Oil Non-Toxic and Safe? (Yes, Sort Of)

This article is a comparison of linseed and tung oils:

• Are they safe and non-toxic?
• What types of chemical additives are used in the different oil types?
• What compounds do they naturally off-gas?
• When do they cure and stop off-gassing VOCs?

I review the following oils:

• 100% polymerized linseed (pure and with a stain)
• 100% Tung Oil
• Rubio Monocoat (plain and a blue color)
• Odies Oil

This article contains affiliate links, upon purchase I earn a commission at no extra cost to you.

Summary:

Safety: Linseed oil and Tung oil in their purest forms are all-natural, food-safe (“GRAS” here and here) and are considered non-toxic, says Dr. Mudgal, Toxicologist. Those sensitive to chemicals may not do well with the natural aldehydes, hydrocarbons, peroxides, alcohols, ketones, and acids that can off-gas during oxidation (curing). Both can be smelled past their cure times (with Linseed oil retaining a smell for longer). Some formulations can contain additives that can introduce toxicity concerns or make them not food-safe says Dr. Mudgal, like Cobalt and Manganese driers, and various solvents.

Best Brands: Out of the brands I tested, Rubio Monocoat is the lowest odor, though we don’t know all of the ingredients. Tried and True makes a 100% pure Linseed oil (polymerized) which requires a solvent for some applications, and Real Milk Paint makes a pure Tung oil, which for most woodworking projects requires the non-toxic, food-safe (but potent) citrus solvent.

Linseed and Tung Oil – Chemicals and Offgassing 

Linseed and Tung Oil are the traditional natural finishing oils for wood – some forms also work well as stone and concrete sealers.

Oils That Don’t Go Rancid

Both of these oils are called “drying oils” which means they polymerize in the presence of oxygen forming a durable and elastic finish.

They do not go rancid like non-drying oils.

Are Linseed and Tung Oil Zero-VOC?

While most of these oils – the pure ones and ones with additives – claim zero-VOC (a legal term), they do give off natural volatile compounds, though they are not technically considered toxic, whether they affect you will depend on you and your tolerance.

Are Linseed and Tung Oil Toxic?

During oxidation (curing) of tung and linseed oil, aldehydes and hydrocarbons, peroxides, alcohols, ketones, and acids may off-gas during oxidation (1).

I could pick up this chemical odor very acutely.

In low concentrations that come off of Linseed and Tung Oil, these are considered non-toxic.

For those who are chemically sensitive, aldehydes especially, can cause reactions. It certainly did cause me symptoms when I had chemical sensitivity.

Are Linseed and Tung Oil Safe for the Chemically Sensitive?

If you are sensitive to odorants be sure to test both in the 100% pure versions, as well as Rubio Monocoat, and see how you do.

For those who like pure natural finishes and who are not bothered by the natural aromatics of plants and oils, both 100% linseed and 100% tung would be great options.

Those who are sensitive even to natural odorants often do not do well with these two oils.

Which One was Less Toxic, Linseed or Tung Oil?

I wasn’t expecting to like Rubio Monocoat, the modified linseed oil, because of the lack of transparency of ingredients, but it turned out to be my top choice for many reasons.

Rubio Monocoat had the lowest odor of all the options I tested for this article.

If that is still too high odor for you, you can also consider other drying oils like hemp or walnut oil, depending on what you are using it for.

Pure Tung 

When choosing a Tung oil, I would suggest looking for 100% pure Tung oil.

Are Tung Oils from the Hardware Store Pure and Safe?

I wouldn’t use the “Danish oil” mixes from the hardware store, or anything premixed with a thinner.

I have not seen a pure tung oil at Home Depot or other large hardware stores (yet).

The Behr tung oil contains petroleum waxes, petroleum distillate solvents, and metallic driers.

Pure, Safe Tung Oil Brands

My top brands for pure 100% tung oil are Real Milk Paint and The Hope Company.

We want to start with something pure that does not have additional chemicals added.

I found the Real Milk Paint Tung to be milder in odor than the brand I initially tested in this post which later changed my view more favorable towards Tung Oil.

Can Tung Oil Be Used Straight Without a Thinner Additive?

Tung oil can be applied without a thinner to weathered wood, old wood, terra-cotta and concrete. (Anything super porous).

Check to see if your application requires a thinner before starting because the thinners are solvents, and they are just about universally more difficult for the chemically sensitive.

What are the Chemical Thinners in Tung Oil and are they Healthy and Safe?

Common thinners for Tung oil are citrus solvent, mineral spirits, or odorless mineral spirits.

100% natural citrus solvent is technically non-toxic but is very potent – it wiped me out and made me sick when I was highly chemically sensitive,

Citrus solvent is mostly made up of d-limonene. If you do well with orange essential oil then you will be fine with low levels of citrus solvent.

For MCS – Based on ten years of working with chemically sensitive folks: chemically sensitive folks should generally not apply it themselves, at least not without PPE, and when you could re-enter or bring in the item depends on your level of sensitivity. I would be cautious not to expose yourself to high amounts if you know you do well with this odor in lower levels so that you do not become sensitized to lower amounts.

When I was chemically sensitive I did better with odorless mineral spirits than citrus oil. Now that I’m recovered, I would go with citrus oil since mineral spirits are not totally non-toxic (toxicity reviewed here).

Is Tung Oil Food Safe?

100% Tung oil is food-safe on butcher block, cutting boards, wooden countertops, concrete countertops, and wooden toys once cured.

(To err on the safe side, wait 30 days for it to be cured).

The food-safe solvent is the citrus solvent.

Where Can Tung Oil be Used/What Surfaces Can it Seal?

Apart from wood, Tung oil can be used on concrete countertops, concrete floors (in some cases), concrete or terra-cotta bird baths, terra-cotta planters, on metal as a protector, and more.

How Long Does Tung Oil Take to Cure?

Generally Tung oil normally takes 30 days for a full cure.

Some companies claim 95-98% cured within 7-14 days and depending on conditions, it can take up to 90 days for a full cure.

The time it takes to cure is not the same thing practically or scientifically as the time it takes to finish off-gassing.

Does Tung Oil Cure/Polymerize Faster than Linseed Oil?

There is a statement on Wikipedia that Tung oil comes to a full cure whereas Linseed continues to polymerize for years.

I was not able to confirm that statement that linseed oil continues to polymerize for years after looking through all the scientific literature on tung oil and talking to many companies.

However, when Tung oil is exposed to oxygen, it undergoes a reaction that results in cross-linking between the oil molecules, creating a durable and waterproof film.

In the literature, I did see lots of references to the idea that Tung oil has a superior ability to polymerize due to its a-elaeostearic acid (77–82%) content.

In theory, this gives it a greater chemical reactivity and excellent ability to polymerize (cure) compared to Linseed oil (2, 3).

Linseed oil, on the other hand, can take longer to polymerize and may not fully cross-link, resulting in a finish that is not as durable.

Comparing Off-gassing of Tung and Linseed Oil

In my subjective assessment, Tung was not as pungent when in liquid form, but they both off-gas similar compounds while curing.

Though the odors during curing of Tung are a little different from Linseed.

Keep in mind: individual sensitivities vary a lot, if you are a lot more sensitive to one of these oils you will perceive it as higher odor (if you have MCS).

My perception at 17 and 30 days found a higher odor of Tung than all of the Linseed oils I tested.

Many sensitive people will still be able to pick up some off-gassing of Tung oil at 30 days.

Linseed Oil – Review of Chemical Additives and Off-gassing

Linseed Oil Comes in Three Types

1.  Raw, which is pure, is not usually used for wood, as it takes a long time to dry and is often cut with a thinner.

2. “Boiled” which has driers, usually metals like cobalt or manganese, or petroleum (which I would want to avoid), this version could be considered toxic if it has toxic metals.

3. Polymerized/stand oil which is pure, food-safe, and faster to dry. This oil does not require a thinner. Polymerized is the type you want to use.

I like the brand Tried and True because it’s pure 100% linseed, and because of their total transparency with ingredients and additives.

Odor and VOCs that Off-gas from Linseed

The odors of Linseed oil (and the citrus solvent) come from their naturally occurring VOCs (4).

The pungent smell of Linseed comes mostly from the aldehydes (5).

Do you Need to Add a Thinner to Linseed Oil?

Polymerized (pure) Linseed oil works for many applications, though Tried and True recommends a solvent for wood floors.

Rubio Monocoat can be used without their Part B – that is, without a solvent – on floors and other wooden areas/furniture.

The solvents/thinners should be tested separately, and are not all tolerable or non-toxic .

How Long Does Linseed Take to Cure?

Linseed will dry within a few days.

However, according to the literature, the drying (curing) reaction of linseed oil continues for many years even when the oil film is effectively dried in a few days (7).

This could explain why sensitive people find that natural linoleum which is heavy in linseed oil can still smell years later when the sun hits it.

You can speed up the off-gassing odor by increasing temperature and decreasing humidity.

Raw Linseed is slower to cure, compared to polymerized Linseed oil or modified oils with driers.

Comparison of Linseed and Tung Oil Off-gassing

Tung oil has milder odor compared to polymerized linseed in my assessment at first, but at the end of the 30 days, Tung had a stronger odor remaining.

Rubio Monocoat (modified linseed with driers) was far less pungent than either polymerized Linseed oil or Tung oil when cured (to my perception).

Surfaces to Seal with Linseed Oil

Linseed oil is mainly used to seal wood, though can be used to seal other porous surfaces.

It can also be used on metal like on tools. (8)

Linseed oil paint works particularly well on items from terra-cotta pots to laminate cabinets, metal objects, brick and concrete, plastic objects, and drywall.

Odies Oil has been used as a concrete sealer which I am quite certain is linseed-based, but the ingredients are not disclosed.

(In the video, I discuss why I think Odies Oil is Linseed-based.)

Is Linseed Oil Mold-Prone?

Woodworkers have varying opinions on the two oils, each camp preferring one over the other with some noting caution to Linseed oil as being less mold resistant in certain conditions.

Outside in high humidity, linseed does not usually do well on it’s own.

Zinc oxide needs to be added to it to make Linseed oil finishes appropriate for high humidity indoor spaces or outdoor conditions.

For indoor space with normal humidity levels, linseed oil will work just fine, and I have no trouble recommending it.

Rubio Monocoat‘s formulas that are suited to outdoor conditions (they have one that is made for exterior applications).

(Though this is the one that we don’t have all the ingredient disclosure for).

Tung oil has the advantage of holding up well to water and mildew outside.

The Outdoor Defense Oil is formulated for outdoor applications and is very mold-resistant. It is made from Tung oil, pine oil, and zinc.

Top Non-Toxic Brands of Linseed Oil

1. Rubio Monocoat Linseed Oil Finish

Rubio Monocoat makes linseed-based finishes (from natural and modified ingredients) that smell like honey or lemony incense.

It contains a wax component (natural and modified) as well.

They claim zero VOCs but you should test any linseed product before using it. (Some Linseed oil products claim <5 mg / l VOCs).

Chemical Additives in Rubio Monocoat

The accelerator which is a Part B drying agent lists hexamethylene diisocyanate as an ingredient (0.5%), but not all ingredients are listed.

Because Part A (without the drier) takes a very long time to dry, it sounds like part raw linseed to me (though it does not smell like raw linseed).

This would mean that Part B is unknown driers and hexamethylene diisocyanate.

It does contain non-aromatic hydrocarbons which they claim are not a solvent.

I could not get the company to claim no metallic driers, though it does say it’s free of the following heavy metal drying agents: arsenic, beryllium, chromium, cadmium, nickel, and lead.

Because they are Toy Safe EN-71 they are free of any substantial amount of aluminum, antimony, arsenic, barium, boron, cadmium, Chromium (III), Chromium (VI), cobalt, copper, lead, manganese, mercury, nickel, selenium, strontium, tin, organic tin, and zinc.

Other metallic driers for oil-based finishes (that they don’t say they are free of) include: calcium, iron, zirconium, and vanadium.

While I do tend to prefer brands that disclose all their ingredients, because this is such a low-odor version of Linseed oil I still have a preference for this brand (this is what I would use if I was finishing floors with a natural oil).

Why Rubio Monocoat Turned Out to Be My Top Choice

Sensitive folks reporting that they really like this brand is important data, and caused me to seriously consider it.

It turned out to be my top pick based on odors, perceived off-gassing level as well as personal tolerance.

I was surprised by how mild it was from start to finish, though I did still pick up a chemical odor at 30 days in the plain color.

I was very impressed with Sapphire which I found cured to my nose at 30 days. 

Because Rubio Monocoat is easy to apply (the only oil floor finish that only needs one coat), is the only oil for floors the doesn’t need a solvent, is easy to touch-up, and seemed to have the lowest odor, much lower than I expected, I have to say it is my top pick.

Performance of Rubio Monocoat

This brand offers unique colors in their stains that few other natural brands offer (greys and white).

Be sure to sample both Part A and Part B as well (though you can use it without Part B), and different colors, which for me tested quite differently.

I tested plain and sapphire.

It also is easy to touch up which is a major bonus.

Cure Time and Off-gassing Time of Rubio Monocoat

Rubio Monocoat (Part A & B mixed) takes one week to cure, they say.

You can use just part A which takes 3 weeks to dry.

Although to me it approached off-gassed at 48 hours, at one week my sense of smell ramped way up (due to a reaction I had to something else), at this point, I could still smell it very noticeably.

So the time that it cures will very much be dependent on you and your level of sensitivity.

2. Tried and True – Polymerized Linseed

Tried and True is my top recommendation for pure linseed with a stain for anywhere you don’t need to add a solvent, because it is totally natural and because of their full disclosure of ingredients.

No driers are used.

It’s only linseed oil (and pigments and/or natural waxes in some formulas).

A solvent is needed for wood floors.

This company will claim that metals are not a component in their formula or pigments, other than what comes naturally from the soil.

Performance of Tried and True – Review

I really liked the look of the Java stain (pictured), it went on beautifully even though I did not sand and prep my wood properly.

That’s going to give you a high-quality stain/finish in one.

I was really impressed with how the stain looked after my disaster trying to mix my own pigments with Hemp oil.

They offer versions with waxes and resins as well, check out the different formulas to see which suits your project.

3. Odies Oil (Universal Finish)

Odies Oil (the Universal Finish) is another oil I tested.

I suspect this to be a linseed-based finish. The ingredients are listed as: lubricating oil, drying oil, natural waxes; essential oil.

They claim solvent-free, that it contains UV inhibitors, and it has the warning for spontaneous combustion (which is seen on all drying oils).

My Experiment to Guess What is in Odies Oil

I made the following mix which came very close to the odor of Odies: odorless mineral oil (a solvent), linseed oil, beeswax, carnauba wax, lemon, and orange oil.

I did not get the exact match but it seemed close, therefore, that is my guess on the basics of what is in Odies Oil.

There is still another essential oil in there I think, lavender or similar – something flowery.

And there is a different mix of waxes I think, compared to my test. But I got quite close to their mix, according to my nose.

Odor and Off-gassing of Odies Oil

This tested quite strong to me at first, with the essential oils being overpowering for me (I’m extremely sensitive to essential oils) in the first 24 hours, but at 48 hours that had faded significantly, and what smelled to me like Linseed oil was then dominant.

Those who are reactive to essential oils might have trouble with this one, but you can see how fast it fades for you.

As always, I’m not a fan of using products that I don’t know the ingredients of, we don’t know if there are toxins in here, but it did cure faster than some of the others.

They claim 2-3 weeks to cure.

4. Other Brands

Oils labeled as “teak oil” or “Danish oil” from hardware stores are usually a mix of oils like linseed or tung, solvents, and possibly resins, UV inhibitors, and mildewcides.

I wouldn’t use those, go with one of these pure brands.

My Test Results

My test results at 24 and 48 hours are in the video.

My testing of Odor at 17 days 

• Rubio 1st place 
• Tried and True Java 2nd place
• Odies Oil and Tried and True still quite noticeable odor, 3rd place
• Tung actually the strongest at 17 days, last place (though I like the Milk Paint version better than the Canadian brand I initially tried).

My testing at 30 days when they should all be “cured”

• Rubio Sapphire – this is the only one that seems totally cured to me at 30 days 1st place.
• Rubio plain – I can pick up the Rubio plain at 30 days though it is very light.
• Odies oil – very slight odor in 3rd place for off-gassing levels
• Tried and True Java in 4th place very slight odor
• Polymerized linseed – Tried and True plain still off-gassing 5th place
• Tung oil – strongest one. I do not agree that Tung oil off-gasses in 30 days, at 30 days I can still pick up the odor of one coat. I kept it at 30 C and about 50% humidity. I cannot say it is 100% off0gassed. Later when I tested Milk Paint brand I was much happier with Tung Oil, and would likely choose it over Linseed.

Other Options for Sealing Wood

This article covers in detail natural oil-based wood floor finishes (which solvents they need, how to apply them etc).

This article covers natural finishes for all wood (not just floors).

That post is also a comprehensive overview of water-based 0-VOC and non-toxic finishes for wood as well as stone and masonry.

Getting Rid of the Odor of Linseed and Tung oil

If you used Linseed or Tung oil and then found the odor is too strong for you we can mostly get rid of the Linseed odor smell with the following techniques.

Corinne Segura is an InterNACHI-certified Healthy Homes Inspector with certifications in Building Biology, Healthier Materials and Sustainable Buildings, and more. She has 10 years of experience helping others create healthy homes. You can book a consult here.

Sources for this Post

 1. EPA 1991 Impact Of Declaring Soybean Oil Exempt From VOC Regulations On The Coatings Program  

2. Modern Technology of Paints, Varnishes & Lacquers (2nd Edition), NIIR Board February 7, 2007, ASIA PACIFIC BUSINESS PRESS Inc. 

3. Meiorin, C., Aranguren, M. I., & Mosiewicki, M. A. (2015). Polymeric networks based on tung oil: Reaction and modification with green oil monomers. European Polymer Journal, 67, 551–560. 

4. Identification and Quantitation of Volatile Organic Compounds from Oxidation of Linseed Oil
Juita, Bogdan Z. Dlugogorski, Eric M. Kennedy, and John C. Mackie. Industrial & Engineering Chemistry Research 2012 51 (16), 5645-5652  

5, 6, 7 Low temperature oxidation of linseed oil: a review. Juita, Dlugogorski, B.Z., Kennedy, E.M. et al. Fire Sci Rev (2012) 1: 3.  

8. https://extension.colostate.edu/topic-areas/yard-garden/tool-care/#:~:text=Linseed%20oil%20and%20camellia%20oil,Wipe%20away%20excess%20oil.