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Ask an Expert: What is thymol, and does it kill viruses?

Last updated: October 30,2020

Thymol is a plant-based ingredient used in natural disinfectants and other products. But does it really kill viruses? Here’s what you should know about thymol.

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Here at Grove, we're big believers in saving the planet with science — and without sacrificing products' effectiveness. To break down how natural and sustainable products manage to stack up against the competitors without questionable chemicals, we're grilling our scientists, doctors, and fellows for Ask an Expert: easy-to-understand primers on how products work. Check back each month for a complex process, simplified.

Natural beauty and cleaning products are better for the environment than their conventional counterparts, and they’re better for our bodies. If you’re new to the world of natural products, you may be wondering whether their active ingredients can hold a candle to the powerful chemicals you’re used to.


Take thymol, for example. This plant-based ingredient is used in a variety of products, including disinfectants. But where does it come from, and can it really protect you against harmful microorganisms — including coronavirus?


We asked our Senior Director of Science and Formulation, Clement Choy, Ph.D. — better known as Clem around these parts — to give us the lowdown on thymol and weigh in with his expert opinion on whether this ingredient is worth your “thyme.”

Q: What is thymol, and where does it come from?

A: “Thymol is an essential oil, but it possesses antimicrobial activity — it’s an active essential oil,” says Clem. “There are other essential oils that have antimicrobial activity but thymol is probably one of the best.” Thymol is found in several botanical oils, including bee balms, some wildflowers, and its herbal namesake, thyme.


Like many other plant-based substances, thymol has strong antiseptic properties. In ancient Egypt, thyme was used for embalming. The Greeks burned it as incense, and the Romans purified their rooms with it — and added it to their cheeses and liqueurs for its aromatic flavor. Native Americans used thyme poultices to heal skin infections and wounds.


When thymol is extracted from a plant, it’s a white, crystalline substance that’s used in a variety of products for a range of purposes.

Q. What types of products contain thymol?

A: Thymol was originally registered with the Environmental Protection Agency (EPA) in 1964 for use as an animal repellent to keep birds, squirrels, beavers, rats, and other critters away without harming them.


Today, it’s widely used as a pesticide. Researchers at the University of Florida studied thymol in the 2000s as a potential replacement for methyl bromide, a powerful soil fumigant that’s effective against a variety of crop pests — but also a powerful ozone depleter, which is why it was banned in the U.S. in 2006. The studies found that thymol kills bacteria that causes wilt and rot in a wide variety of plants, and it’s effective for controlling some soil-borne fungi that damage crops.


Thymol is also used in mouthwashes and other dental products, thanks to its ability to fight tooth decay and infection, prevent gum disease, and fight bad breath. It’s also used in perfumes, disinfectants, and food flavorings.


Thymol is regulated by the EPA under the Federal Insecticide, Fungicide, and Rodenticide Act. It’s also regulated by the Food and Drug Administration (FDA) under the Federal Food, Drug, and Cosmetic Act.

Thymol and cleaning

Q: How does thymol kill bacteria and viruses?

A: Thymol kills bacteria by disrupting the cell walls and cell membranes, causing the cell contents to leak out and the bacteria to die. Enveloped viruses like SARS-CoV-2 — more commonly known as the coronavirus — have a protective fatty coating, which is vulnerable to disinfectants like thymol, which break down the protective shell and deactivate the virus. Viruses like the norovirus, which has a tough protein shell, are harder to deactivate and require a longer exposure to disinfectants.

Q: Are thymol-based cleaners as effective as chemical cleaners like Lysol and Clorox for protecting against viruses like coronavirus?

A: “The category of disinfectants is pretty restrictive, and it’s always been dominated by Clorox and Lysol,” says Clem. “These are quaternary ammonium compounds — very effective for killing viruses and bacteria.” Unfortunately, they’re also associated with respiratory, developmental, endocrine, and reproductive effects. Depending on the specific product, a disinfectant needs to be in contact with a surface for anywhere from four to 10 minutes in order to kill the touted 99.9 percent of germs.


The EPA has approved a number of thymol-based disinfecting cleaners — including several Seventh Generation products with a 0.05% concentration of thymol — for killing 99.9 percent of household germs, including SARS-CoV-2. For the best results, thymol-based products should come into contact with a surface for 10 minutes (including drying time) to eliminate tough germs like E. coli and salmonella, which are far harder to kill than SARS-CoV-2.

Q: Why do cleaners/wipes with thymol smell strange/pungent?

A: Thymol isn’t the best-smelling substance you’ll ever encounter. It’s described as phenolic, medicinal, camphor, woody, and spicy. Some people find this odor downright offensive, but others don’t mind it. The scent of thymol is natural, and even if it’s unpleasant, it’s harmless — unlike synthetic fragrances found in other popular chemical disinfectants. Many products containing thymol are bolstered with other essential oils that make it smell better.

The effects of thymol on people and the environment

Q: What health effects does thymol exposure have on humans?

A: Thymol and thyme essential oil are listed by the FDA as foods for human consumption and food additives. They’re both categorized as Generally Recognized as Safe — or GRAS — and as such, they’re non-toxic to humans. However, at high concentrations, thymol can irritate the skin and lungs.

Q: What effects does thymol have on the environment?

A: Thymol is non-toxic to animals and aquatic life, although it’s deadly to microorganisms. Thymol is not considered an environmental toxin. It bio-degrades rapidly in the environment through normal processes.

Disinfectant terms you should know

Antimicrobial

Antimicrobial products kill or slow the spread of microorganisms, also known as microbes. Microorganisms include viruses, bacteria, protozoans, and fungi. The EPA regulates antimicrobial pesticides, which are used to kill microbes on countertops and other surfaces. The FDA regulates antimicrobial antiseptics, which are used to kill microorganisms on people, pets, and other living things.

Antibacterial

Antibacterial products kill or reduce bacteria. Antibacterial chemicals like triclosan and antibacterial soaps and lotions kill most bacteria, but some may survive. Those that survive can become antibiotic-resistant, which is a major public health issue, since antibiotic-resistant strains of bacteria can increase the risk of infection in the community. Thymol has been found to increase the susceptibility of some bacteria to antibiotics, making it a better disinfecting alternative.

Antifungal

Antifungal agents selectively eliminate fungal pathogens like mold and yeast. Fungi, like bacteria, can become drug-resistant with exposure to antifungal agents. Recent research shows that thymol and thyme oil, used alone or with antifungal drugs, can act against drug-resistant strains of Candida.

Expert Tip

Cleaning versus disenfecting

Cleaning and disinfecting aren’t the same thing. Cleaning is the process of removing dirt and germs from surfaces. Cleaning doesn’t kill germs, but rather reduces their numbers and therefore the risk of spreading an infection. Disinfecting is the process of killing germs. It’s important to clean a surface before disinfecting, since dust and grime can prevent a disinfectant from fully coming into contact with the microbes.

Shop thymol-based cleaners

Looking for more cleaning how-tos and other sustainable swaps you can make at home? Grove has you covered with our buying and cleaning guides. And let us know how if you have any cleaning questions (or share your own tips using #grovehome) by following Grove Collaborative on Instagram, Facebook, Twitter, and Pinterest.

If you're ready to take on germs, shop Grove Collaborative's cleaning essentials for the cleaning tools to tackle the job.

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