Summary: Toxicity Concerns In Wax Melts:
The data and sources for this are below.
- The wax type is not all that important here, though beeswax is my least favorite; soy and coconut are preferred – avoiding paraffin is not nearly as important as it is in candles (where we are burning it). None of the most harmful PAHs are volatile at 180°F, therefore any wax is OK on the PAH front for wax melts. Soy and coconut are preferred for me (organic and even non-organic would still be preferred), for low PAHs, and low to no pesticides. Beeswax is high in PAHs (though not the most toxic ones), and higher in concerning pesticides than other waxes. Beeswax is my least preferred wax due to PDCB pesticide residues, which are volatilized in (especially non-organic) wax melts (though this is still at quite low levels).
- Both fragrance types give off VOCs and nanoparticles, I have a slight preference for natural fragrance – both 100% essential oil-based brands, and conventional brands are terpene-heavy. This creates, at times, high VOCs and nanoparticles in the air (more than we would see naturally outside). Because synthetic fragrance formulations use terpenes plus introduce additional chemicals of concern, I would still stick to all-natural essential oils here. You can reduce harmful chemical reactions by airing out the home prior to using the wax melts.
- Dyes are not a concern because none are substantially volatile/toxic at 180°F or in this application.
- I would avoid added phthalates, but 100% phthalate avoidance may not be possible here – synthetic fragrance, when made with phthalates (which is much less common now), has a substantial level of phthalates; essential oils contain trace to significant amounts of phthalates; beeswax numbers are low (we don’t have the exact number); coconut wax and soy wax have trace phthalates; paraffin wax we don’t have numbers for, but we expect it to be trace.
- They are not meant to be used in unventilated spaces – interestingly enough, many brands, especially the large brands, say to “use in well ventilated room”. Presumedly due to the VOCs and or nanoparticles created. But I don’t know anyone that would introduce a scented product and then open the windows, since that conflicts with the goal of using wax melts. Keep that in mind, that technically, wax melts may not be considered completely safe for all people and pets in normal use conditions indoors (without ventilation).
- Wax melts are not necessarily safer than candles – wax melts are safer in terms of combustion products, but release more airborne scent compounds (VOCs) compared to candles.
The research behind this summary took 20 hours. See the data below for a more detailed discussion and sources.
Safer wax melt brands can be found here.
Toxicity Review of Wax Melts
PAH, Pesticide, and Phthalate Content in Waxes
In the wax component alone, we want to consider polycyclic aromatic hydrocarbons (PAHs), pesticides and phthalates.
SUMMARY: PAH Comparison Between Wax Types
On the basis of general PAH volatility data (e.g., benzo[a]pyrene melts around 178 °C, boils near 495 °C, and has negligible vapour pressure at room temperature and the fact that 4–7-ring PAHs are effectively non-volatile while only 2–3-ring PAHs readily evaporate), the most carcinogenic heavy PAHs present in any of these waxes (like BaP or chrysene) are not going to meaningfully volatilize at wax-melt temperatures around 180 °F, so inhalation exposure from melts comes mainly from lighter, less potent PAHs. (Source)
Beeswax tends to have the highest total PAHs (including more of those lighter ones), so its low-toxicity PAHs do contribute some exposure, but they’re still a very small addition compared with everyday PAH intake from food and ambient air.
SUMMARY: Pesticide Comparison Between Wax Types
- Paraffin does not contain pesticides
- Soy oil can contain pesticides, refining it removes most of it and then we would expect processing it into wax to remove even more, leaving trace pesticides, most likely (though we found no study just on the pesticides in soy wax itself). Organic brands are best, but not a dealbreaker for me here.
- Coconut oil is expected to have zero to an insignificant amount of pesticides since the oil itself often has no pesticides or they are removed in deodorizing. (source, source, source), the wax has even further processing.
- Beeswax contains pesticides (source, source and source). The most worrisome pesticide is p-dichlorobenzene (PDCB). In a recent study the concentration was 0.22 mg/kg. This is volatile in wax melts, though it’s much lower than the levels would be if you used mothballs in your house (Dr. Amine says beeswax PDCB residues is negligible compared to the intentional use). Organic beeswax is better.
- Essential oils – also contain some pesticides but often really low, except in some citrus oils. Even then, the level is low compared to food exposure, says Dr. Amine.
Sources
- Paraffin wax for candles is refined or semi-refined, usually meeting either FDA 21 CFR 178.3710 (indirect food grade) or REACH, from what I saw.
- Soy wax, made from hydrogenated soybean oil, also contains some PAHs.
- In one study, they found the mean of 1.55 micrograms per kilogram BAP, 8.28 micrograms per kilogram PAH4, 11.97 micrograms per kilogram PAH8, 103.82 micrograms per kilogram for PAH15, and 3.38 micrograms per kilogram for TEQBAP. Removing the overlaps, which totalled around 100 micrograms/kg.
- I could only get numbers from soy oil; the process of producing wax from the soybean oil removes some PAHs.
- Beeswax, being a natural product exposed to environmental pollution, tends to contain more PAHs. In one study, the total sum of PAHs ranged from 324.0 to 866.4 μg/kg; the highest content of PAH4 (benzo[a]anthracene, chrysene) was 21.0 μg/kg. Another study also found PAHs in beeswax with Naphthalene at the highest presence and concentration (an average of 0.296 mg/kg).
- Beeswax also contains pesticides and phthalates (DEHP) (source and source).
- The most worrisome pesticide is p-dichlorobenzene (PDCB), in a recent study the mean concentration of the positive samples was 0.22 mg/kg.
- Coconut wax can contain PAH levels.
- In one summary study, one source of coconut oil levels came in at 4.4–6.6 μg/kg PAH4. PAH levels are reduced when it’s processed into wax.
- Note: Candles and wax melts are not 100% coconut. This wax is blended with soy, apricot, paraffin, rapeseed, etc.
Are Dyes Toxic?
Some azo solvent dyes with carcinogenic potential are still manufactured and sold for coloring wax and candles by candle supply stores.
At typical wax-melt temperatures (around 180 °F), those dyes are essentially non-volatile solids with negligible amounts given off at wax melt temperatures.
Plus they are only generally a risk when ingested or with prolonged skin contact.
Anthraquinone dyes and Quinoline yellow, other potentially harmful to health types of dye, are effectively non-volatile at 180 F.
Are Fragrances & Essential Oils Toxic in Wax Melts?
Compared to traditional candles, wax melts release more airborne scent compounds since direct heating maximizes the melted surface area.
“Therefore, counterintuitively…. the particle number-based inhalation exposure associated with non-combustion-based scented wax melts is similar to those posed by combustion-based scented products like candles and gas stoves,” they say in this study on nanoparticles.
The study looked at the terpene/terpenoid fragrance molecules that come off wax melts and what byproducts they produced in the indoor air when heated.
Terpenes/terpenoids are natural compounds or nature-identical synthetic molecules.
This study, therefore, is relevant to wax melts made from 100% natural fragrances and conventional fragrances (which are almost always a mix of natural or nature-identical compounds like terpenes and more purely synthetic compounds).
The VOCs released from wax melts primarily consist of monoterpenes and their oxidized forms, monoterpenoids.
In indoor environments, these VOCs can react with ozone, resulting in the nucleation and subsequent growth of nanoparticles.
Formaldehyde, other carbonyls + SOA
Many natural or nature-identical compounds used on both natural and synthetic wax melts increase formaldehyde, secondary organic aerosols in the air.
Ozone–terpenoid reactions produce carbonyls such as formaldehyde and acetaldehyde, organic acids, hydrogen peroxide, secondary organic aerosol, and hydroxyl (OH) radical.
Subsequent reactions of OH with volatile organic compounds (VOCs) can generate additional products (source)
Some of these, like those from linalool, as one example, are toxic (source).
Is this different than what happens outside?
The same process happens outside. Terpenes from the forest and plants react with ozone, and there are nanoparticles that result from this.
What’s different inside is that it’s much more concentrated indoors, and there can also be a different chemical mix inside (low nitric oxide in winter for example), and so more nanoparticles can be produced.
Phthalates
Phthalates are found in many essential oils and in some synthetic fragrances used in wax melts.
Diethyl Phthalate (DEP), is the phthalate used in synthetic fragrances for candles and melts, normally.
And phthalates are semi-volatile – heating them up increases their volatility and so more will be found in gas form (source).
Phthalates are also found in beeswax (source).
In wax melts the range of heat is 129 – 170 F (Scentsy), 150 – 167 F (Scentsastionals), 160 – 180 F (for Happy Wax).
Phthalate levels across fragrance types:
- In wax melts I found evidence that phthalates composed 1-5% of some wax melts (source, source).
- Essential oils can have 40 ppb to 13,029 ppb (0.04-13.029 mg/kg) phthalates. Another source shows 16-18 mg/kg in some essential oils (source and source).
Phthalate levels across wax types:
- Beeswax – less than 0.5 mg/kg (source).
- Coconut Wax – using oil as a proxy (though wax could very well have less due to processing) 0.015–0.058 mg/kg (source).
- Soy Wax – using soy oil as a proxy (though wax is likely better) – 0.015–0.058 mg/kg (source).
- Paraffin Wax- I found no numbers for phthalate content in paraffin wax. It’s not an inherent component or intentionally added, but I could not find numbers on if there is unintentional contamination.
Are essential oils better than synthetic fragrances?
There are a number of synthetic fragrance ingredients that are very problematic (they add environmental and endocrine/phototoxic dimensions) and so my preference would not be to move to synthetic fragrance.
Synthetic fragrances also have added UV stabilizers, some of which are toxic. Whereas the brands using essential oils don’t usually add these from what I have seen.
Realistically, moving to synthetic fragrance would not solve the problems of essential oils, because the vast majority of fragrances, and all synthetic wax melts that I saw, are using the typical mix of terpenes plus synthetic ingredients.
So moving to synthetic fragrance brands would not eliminate the terpene -> VOC and nanoparticle problem. It would also not eliminate the natural fragrance allergens.
Are Wax Melts Toxic to Pets?
Some essential oils are toxic to use around pets, see full list here.
Wax melts should be kept away from pets to avoid licking or eating them but this review section focuses on potential effects of the normal use of wax melts and the inhalation of the VOCs.
Pets in General
A few brands use this phrase to avoid liability “We encourage you to contact your veterinarian with any questions or concerns.”
Some companies say their wax melts are safe to use around pets but keep in mind most have a warning about ventilation, that you need to use the wax melts in a well ventilated area.
Yankee says “Home Fragrance products are a great addition to homes with pets and can be used safely around animals with appropriate supervision.”
Happy Wax believes their products are safe for pets, though in another post they say not to use them around birds.
Many other companies share misinformation – that paraffin wax in wax melts would be harmful to pets compared to beeswax or soy, and that essential oils are safer because they are natural. Neither of these is true based on the data I compiled.
Allergic reactions:
Some companies also point out that, just like some people, some pets may have allergic reactions to ingredients that are well tolerated by the majority of others.
Happy Wax believes their products are safe for pets, though in another post they say not to use them around birds.
Cats Are Particularly Susceptible to Some Essential Oils
Dr. Mahaney says “cats have had an increase in feline asthma as a result of living in households where there are air fresheners, incense and cigarette smoke—or even just the aroma of cleaning products.” says PetMD.
Vet/toxicology sources consistently flag the following essential oils as problematic for cats, especially when inhaled in a closed space, applied to skin, or ingested: Wintergreen, oil of sweet birch, citrus oil (dlimonene), pine oils, ylang ylang oil, peppermint oil, cinnamon oil, pennyroyal oil, clove oil, eucalyptus oil, and tea tree oil. (source)
Cats and Dogs
Happy Wax says that essential oils are only harmful to cats and dogs if the essential oils are ingested by the animal or if the essential oils are rubbed directly on the skin.
They continue: The risk is greatest when essential oils are in their purest (liquid) form. … So as long as you are using our wax melts for their intended purposes, there are no issues with using them.
Dr. Amine says that if you don’t use them that often and if they don’t ingest it then it is safe.
With Birds, You May Not Want to Use Wax Melts At All
There is mixed information from companies on birds.
Birds are especially sensitive to essential oils (source and source), some vets and some of the wax melt companies like Happy Wax recommend against using essential oils, including wax melts, around birds completely. (source)
Other recommendations are aimed at air fresheners in general (that it’s better not to use them around birds) PetMD says.
Essential oil diffusers are much more concentrated than wax melts, and those are not recommended around birds, says the BC SPCA. Sometimes the recommendations for wax melts in particular are not clear.
Other companies like Scentsy say if “products are used for their intended purpose, there should be no adverse effect on indoor birds or other pets. For safety purposes, Scentsy recommends that warmers be used in a well-ventilated room. If your customer has a small indoor bird, ask them to consider leaving a window or door open when heating wax, or using their warmer for a few hours each day and then turning it off at night. Recommend they consult their veterinarian with any concerns about using Scentsy products around their pets.”
Other Pets
For more exotic pets, we recommend consulting with your vet first.
Review of Specific Brands:
Are Scentsy wax melts toxic?
They use a paraffin wax blend, mix of synthetic and natural fragrance, and some Scentsy Bar fragrances contain diethyl phthalate (DEP), they say on their website, at the time of writing.
Under the FAQ section about pets, they say the wax melts should be used in “a well ventilated room”.
- Yankee Candle Wax Melts – made with paraffin wax, and natural and synthetic fragrance ingredients. They don’t list other ingredients apart from the wax and fragrance. They do not mention if they use phthalates or not.
- Febreze Wax Melts – Febreze does not use phthalates in any of their products. The wax melts are made of a Wax Blend, Fragrances, Synthetic Wax, Benzophenone-12, Octrizole, Colorants. “Use only in a well-ventilated area”, they say.
- Glade Wax Melts – Their scented wax melts are made without phthalates, parabens, formaldehyde and nitro musks. They are made from paraffin wax, a mix of natural and synthetic fragrance ingredients, and more here. “Do not use in small, confined areas without adequate ventilation”, they say.
- Happy Wax Wax Melts – Soy wax, phthalate-free essential oil-infused fragrance oil, dye. Notice that it says essential-oil-infused (synthetic) fragrance oils. Some of the Amazon listings say: “Use only in well-ventilated areas”.
- Walmart Wax Melts – Better Homes and Gardens Wax Melts – wax, UV stabilizer, dye and fragrance, so we don’t know much here, we don’t know the wax type but most importantly, we don’t know if it contains phthalates. Mainstays Wax Melts also don’t list the ingredients online.
Non-Toxic Wax Melt Brands are here.
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.
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