17 natural insect repellants in home made soap making: As proven by science

The past few weeks I’ve had a new problem which I’ve never had to deal with in my life before. I don’t know if it’s because I’m heavily pregnant (do the hormones change the way I smell?) or if the wasps in Donegal are just more persistent than the rest of the world, but I keep getting them showing way too much interest in me.

I actually got stung by a bee for the first time in my life last week! I was stuck at some roadworks and a bee flew between my dress and the car seat. I had no idea it was there, so when I leaned back to wait for the line to move, it stung me! Usually, insects avoid me. So I started wondering about natural insect repellants.

Being a scientist at heart, I couldn’t just buy any random essential oil rumored to work as a natural insect repellant, so in this article I’m going to give you an overview of the scientific evidence with links back to the original research so you can investigate for yourself which essential oils make the best insect repellants for soapmaking.

The factors affecting how effective an essential oil is as an insect repellant:

One of my favourite articles on this topic is a really detailed meta-analysis done by Maia and Moore in 2011, where they compared the results of a huge number of studies done on essential oils including citronella, neem, and the pine/cedar and mint families of essential oils. They found varying effectiveness. The main factor affecting how well an essential oil worked as an insect-repellant was the type of insect. Even different sub-species of the same insect could react differently to the same oil.

For example, two different types of mosquitoes are An. Arabiensis and An. gambiae. Studies have shown that citronella oil gives 90% protection from An. Arabiensis for 6 hours, and 100% protection from An. Gambiae for 6-7 hours.

Another example is thyme (variety: thymus vulgaris). This was found to offer 100% protection against An. albimanus for up to 105 minutes while it only offered 91% protection against C. Pipiens sallens for 65 minutes in a different study.

The concentration of the various natural compounds in an essential oil also makes a difference to the effectiveness. Using the above example again, thymus vulgaris offered 91% protection against C. pipiens sallens for 65 minutes when it was applied topically (directly on the skin) as linalool. When it was applied topically as thymol, it offered 91% protection for 70 minutes against the same insect. And when it was applied topically as carvacrol, it offered 95% protection for 80 minutes against the same insect.

This shows that different compounds in the essential oil can make it more or less effective. For best results, you need to ensure your essential oils are top quality and not diluted with any other compounds before you add them to your soap.

So if you’re looking to repel a specific type of insect, such as headlice, wasps or mosquitoes, it’s worth reading through this article to find out what will work best.

Which common essential oils work best as general insect repellants?

Citronella:

Citronella is widely known to be an excellent insect repellant. And now studies have been done to support this. The Israel Medical Journal published a double-blind study showing that, when citronella was used on school-age children, 12% got headlice, compared to 50% of the control group (who didn’t use citronella). That’s a reduction of 76%! Article here. It was also studied extensively in the article I discussed above, by Maia and Moore.

Neem:

Neem oil is well-known as an insect repellant. It has been shown to repel mosquitoes effectively by Sharma et al (1993) who found it provided 100% protection for 12 hours against mosquitoes. They mixed the neem oil with coconut oil then applied it directly to the skin. The results were published in the Journal of the American Mosquito Control Association. Article here.

In a second study, researchers looked at how effective neem oil was for repelling headlice. The study can be criticized as it had a complicated design measuring multiple factors at the same time (making it impossible to control variables), and a very small sample size (only 47 participants in total). The results showed combing with conditioner alone was 25% effective in removing lice while combing with conditioner and using neem oil was 35% effective in removing lice. The results were published in Advances in Pediatric Research. Article here.

Potentially confounding factors that made this research not very scientific include: The age of participants. Anyone from 6 months to elderly could participate. The participants were recruited from the local area and had to have at least “one headlice” to participate. Obviously, the treatment for someone with a mild headlice infestation or “one headlice” is going to be significantly easier than dealing with a severe infestation that has affected someone’s entire family for months. The home situation was not considered: It wasn’t considered whether pillows, bedding, towels etc were causing re-infestation before the person had been assessed as “cured”. In a home where multiple participants all have lice, the whole family should have been treated together and this was not done because they excluded anyone with specific hair treatments (e.g. coloured hair) and they didn’t control for cleanliness of the house, or sharing of hairbrushes, hats etc, all of which would cause re-infestation. So overall, I’m not happy with the lack of rigour of this study but it’s a great example of why “proven” results don’t always work the same way in real life.

In another multi-study review, Rossini et al (2008) found that neem oil had documented anti-lice activity. Link here. And in an analysis comparing evidence for neem oil and other natural oils for headlice, Heukelbach et al (2007) found that neem oil had an effectiveness of over 98%, repeated across two different studies. Unfortunately, the natural oils they looked at in this study were often mixed into other products so it’s not clear if it was the essential oils or other ingredients in those products that got results.

Tea Tree Oil

Tea tree oil is sold almost everywhere in the UK and Ireland and I think a lot of people use it to try and repel head lice. Di Campli et al (2012) found a 1% concentration of tea tree oil killed 100% of headlice within 30 minutes, and a 2% concentration also killed 50% of lice eggs (full article here).

In other parts of the world, it’s used against other insects. In a study in Indonesia, researchers showed tea tree oil repels and even kills T. castaneum (commonly known locally as the red flour beetle). Research results here (this will download a PDF file from the researchers, as the researchers haven’t put this on a web page for some reason).

Meanwhile Fonesca-Santos et al (2016) researched whether a commercial mosquito repellant could be made from tea tree oil and found it was very effective against the A. aegypti breed of mosquito. You can read about it here.

Great, but what about using essential oil to repel wasps?

Wasps are my main concern right now. We had two more in the house while I was researching and writing this article, today, and I’m so tired of ejecting them.

A study was done by Boevé et al (2014) to assess whether essential oils worked to repel wasps. They tested many different essential oils alongside conventional chemicals, and repeated their tests several times with different wasps, which makes the study more reliable. They found winterberry oil (galutheria procumbens), marjoram oil (o. marjorana), anything from the artemisia genus (over 400 species of plant, including tarragon and mugwort) and wild mint (m. arvensis) were all highly effective at repelling wasps (more effective than DEET, in fact). As far as chemical compounds go, they tested linalool (a natural chemical found in a lot of citrus plants, including citronella) with good results too. You can read about it here.

In another study by Zhang et al (2012), 21 different essential oils were tested to find out how effectively they repelled wasps (if at all). 17 of the essential oils were found to be highly effective, including clove, pennyroyal, lemongrass, ylang ylang, spearmint, wintergreen, sage, rosemary, lavender, geranium, patchouli, citronella, Roman chamomile, thyme, fennel seed, anise and peppermint. Read the full study here.

And finally…

As you can see, there is a huge amount of rigorous, repeatable, reputable scientific evidence proving that essential oils can make excellent insect repellants. For soapmaking, this gives you tons of options for making soaps that are insect repellent but which also smell nice. From my own experiments in this area, I recommend combining no more than three essential oils in one soap. Don’t try to make one soap that repels everything.

I suggest you make a test batch and try it on yourself in the shower before making a bigger batch to give to friends and family, as some of the strong insect repellant essential oils can also be irritants in soap or shampoo bars. For the same reason, you may want to reduce the amount of essential oil in your soaps to avoid ending up with itchy skin. Lastly, be extra-careful using any potent essential oil or other insecticide on children’s sensitive skin.


Recommended for you:

10 ways to get essential oils to be more intense in your soap (melt and pour and cold process)

So you’re probably looking for how to get your essential oils to be more intense in your soap. You might be making cold process soap or melt and pour soap. Maybe you’ve made some homemade soap with pure essential oils and it didn’t come out with a strong scent, or perhaps you’re planning your first homemade soap making project and are hoping to execute a perfect first-time soapmaking recipe…[read more]

How to safely use essential oils in home-made soap (infographic)

Essential oils can cause harm if used incorrectly because they are potent substances. Putting the essential oil on the skin neat (undiluted, or straight from the bottle) causes irritation and can leave your skin burnt. The oil is diluted in soap to a rate of about 3% (average) which makes it less likely to…[read more]

All about essential oils in melt and pour soap (infographic)

Essential oils are often put into homemade melt and pour soap. They can create delightful fragrances that make your soap feel more luxurious. But there’s a lot to know about essential oils in soap. A lot of articles only focus on cold process, ignoring melt and pour, despite the fact melt and pour is a better choice for people with young children, pets or making soap in a campervan.

When I started soaping, I assumed essential oils would behave the same way in cold process soap and melt and pour soap, but this is not true. I have experimented with a lot of different essential oils and found…[read more]

How to safely use essential oils in home-made soap (infographic)

Essential oils can cause harm if used incorrectly because they are potent substances. Putting the essential oil on the skin neat (undiluted, or straight from the bottle) causes irritation and can leave your skin burnt. The oil is diluted in soap to a rate of about 3% (average) which makes it less likely to cause irritation although some sensitive souls are still allergic to some essential oils even at this low concentration.

Check out the infographic and follow these tips to use essential oils safely in home made soap:

1. Buy from a reputable seller

This is the most fundamental first step. It’s not always easy to spot a fake, especially because they’re being sold online where you can’t inspect the product.

A clear bottle is a dead giveaway as genuine oils degrade in sunlight so have to be stored in dark bottles (amber is most common).

The label or online listing should tell you the Latin name. There are many oils with the same common name. If you can’t see the Latin name anywhere in the product listing, there’s a chance the oil isn’t the one you expect it to be, which will ruin your blend at best, and at worst, could cause skin irritation because you might use the wrong quantity.

The listing should always tell you the country of origin. For example, “French lavender” might say “Product of Hungary” at the bottom of the page. This would make it apparent that it wasn’t genuine French lavender from France.

Of course, real malicious fakers and counterfeiters would not honestly write “Made in Kevin’s backyard out of olive oil and artificial lavender fragrance” so the most important thing to weigh up is whether you believe the website you’re shopping on is genuine, or in the case of Amazon, whether the seller is genuine or not. Product reviews can very easily be manipulated so don’t rely on them alone. Soapmaking groups online can help warn you against scams and recommend genuine, reputable suppliers.

2. Always follow the recommended quantities

The FDA and EU both have guidelines about the amount of any fragrance (including natural essential oils) you can use in cosmetics. Usually this is somewhere between 1-5% depending on the oil and its potential toxicity. It’s very easy to want to use more essential oil when your soap hasn’t turned out very strong smelling, but there are other ways to solve this problem. Check out my article 10 ways to get the fragrance to show up in your soap.

3. Do not overheat (above 50 degrees) and ideally keep under 40 degrees (102F).

Overheating oil causes it to release free radicals as the oil’s fatty acid chains break up. Free radicals are carcinogenic as they contribute to cell oxidation. Overheating an oil is the fastest way to change it from safe to dangerous.

When an oil gets too hot, it also loses its fragrance, which is another great reason to take care over the temperature.

4. Do not eat!

This should be self-explanatory but some people do try and eat (or drink) essential oils. Unless they have been certified for food use and sold as such, it’s best not to risk it, especially when it comes to children. Just because something came from a plant, that doesn’t make it safe. All the traditional poisons of Greek tragedies were plant-based.

Conclusion:

Essential oils can be safe in soaps if you take care and follow some simple guidelines. If you need to check any information e.g. chemical compounds present in your essential oil or the maximum concentration for use in various cosmetics and soap making, contact the seller for the product safety documentation (or download it from their website if they’ve made this easy. The Soap Kitchen makes this very easy, as an example of best practice).

Sources:

Turek, C and Stintzing, F (2013) Stability of Essential Oils: A Review https://onlinelibrary.wiley.com/doi/full/10.1111/1541-4337.12006

Bejar, E. (2019) Adulteration of Oregano Herb and Essential Oil https://www.researchgate.net/profile/Ezra_Bejar/publication/337113671_Adulteration_of_Oregano_Herb_and_Essential_Oil/links/5dc5cb74a6fdcc5750348535/Adulteration-of-Oregano-Herb-and-Essential-Oil.pdf

Check out my other articles about essential oils in soaps:

All about essential oils in melt and pour soap (and infographic)

How to get the essential oil scent to show up in soap

History of essential oils in soap

How to make soap: Everything you need to know to make soap even in a campervan.

Here’s a selection of my other articles about making home made cosmetics:

Vegan green tea shampoo bar recipe

Vegan hair conditioner bar recipe

One-ingredient avocado face mask recipe

Easy melt and pour breastmilk soap recipe

At-home DIY facial for new mamas!

10 ways to get essential oils to be more intense in your soap (melt and pour and cold process)

So you’re probably looking for how to get your essential oils to be more intense in your soap. You might be making cold process soap or melt and pour soap. Maybe you’ve made some homemade soap with pure essential oils and it didn’t come out with a strong scent, or perhaps you’re planning your first homemade soap making project and are hoping to execute a perfect first-time soapmaking recipe.

Here, I’m going to go through ten ways to get essential oils to be more intense in your soap. These methods for increasing the scent of your soaps are all based on principles of chemistry. Essential oils are volatile compounds which means they evaporate easily. That’s actually why we love them! They wouldn’t smell so good if they weren’t made exactly the way they are by nature.

Getting a stronger essential oil fragrance in soapmaking is one area where melt and pour soap really outshines cold process, and is one of the reasons I prefer melt and pour soap. Secretly, I think a lot of soapmakers prefer melt and pour, but it’s more profitable for them to write about cold process because it takes more skill to make it (so there’s more to write about).

Essential oils do really well in melt and pour soap. Cold process soap tends to eat the fragrance. But these are not hard and fast rules. It took me several attempts to get lavender essential oil to show up in my melt and pour soap.

If you look at my infographic on essential oils in soap, you’ll see the results I got when I tried a range of essential oils in melt and pour soap. Lavender oil was particularly problematic in melt and pour, and I’ve written a separate article on this.

1. Have you used the correct amount of your pure essential oil in your soap?

This is the easiest fix! All handmade essential oil soaps require different quantities of essential oils to get the perfect fragrance. Bramble Berry’s Soap Queen blog has a fragrance calculator that can help you out. You can find it here.

2. Add a clay as this can hold the fragrance in the soap.

Typically, this works to intensify the scent of essential oils in cold process soap, but I found it made a noticeable difference to increasing the scent of melt and pour soap too. French clay, kaolin and bentonite are all great choices, but some of them will colour your soap so be sure if you plan to sell your soap that the colour matches what you would expect for the scent (e.g. yellow-coloured lavender scented soap would probably be a bit confusing, but yellow-coloured lemon soap or grey lavender soap would make more sense). I prefer French clay and it produces interesting muted colour effects in transparent melt and pour soap base (you end up with a beautiful translucent glow).

3. Is your soap getting too hot?

For melt and pour, it’s easy to overheat the soap while you’re trying to get it to melt, particularly if you use a microwave (which is another good reason to make melt and pour soap without a microwave). For better results, don’t add the fragrance until the soap has cooled to about 37 or 38 degrees celsius. For cold process, pack your soap with ice packs to keep it cool. If you absolutely need your soap to go through gel phase (where it gets very hot), you might have to just accept that your soap won’t smell very strongly if you use essential oils.

4. Consider using a blend of essential oils instead of one individual oil in a soap recipe.

If you have a base note, a middle note and a top note, the fragrance is more likely to permeate the soap in a more nose-catching manner. An example would be lavender as the base note, chamomile as the middle note and lemon as the top note. There are other ways to blend essential oils (you can blend them by effect, e.g. for sleep you might use lavender, chamomile and valerian, or you can blend them by group, e.g. you might want an overall citrus scent incorporating lemon, ten-fold orange and citronella. Different scents have different volatility (evaporation point, which is when fragrance is unleashed from your soap), so a blend of oils will mean your soap has a nice scent regardless of the air temperature, pressure or humidity.

5. Consider using melt and pour instead of cold process, and avoid hot process entirely if you want your essential oils to smell more strongly in your homemade soap.

There is more going on during soapmaking than the soap getting hot. The process of oils turning into surfactants (cleansers) is called saponification, and this is a chemical reaction. The heat is just a byproduct.

6. Wrap your soaps in something as soon as they are able to be unmoulded.

The wrapping needs to be something that doesn’t let oxygen in. I’ve gone through twenty alternatives to plastic for wrapping soaps in this article.

7. Burn incense when you make soap.

Sounds crazy, right? But from a chemistry point of view it makes sense. Scent escapes because it goes from an area of high concentration to one of low concentration. If the air in your soapmaking place is already saturated with a smoky scent, such as an incense stick (not the scent of an oil diffuser) you can prevent scent loss in the same way smoked salmon’s flavour is sealed into the fish (only, you don’t want your soap to smell of smoke which is why you don’t want to go too far with this method). This is a balancing act because you must always follow ventilation safety when working with chemicals.

8. Let your soap harden (and cure) near a dehumidifier or a big bowl of rock salt.

An electric dehumidifier or a big bowl of rock salt will pull the moisture out of the air, which means the scent will have nothing to evaporate into, so it will remain in the soap for longer.

9. Add a sea salt such as Himalayan pink sea salt to your soap.

Himalayan pink sea salt looks beautiful in cosmetics, and especially when it’s embedded in bars of homemade soap. The pink crystals sparkle in bright lights giving your soap an ethereal quality.

Himalayan sea salt will work as a nice exfoliant as well as helping stop the scent escaping. Just don’t put big chunky pieces of salt into a facial soap or you will get redness.

10. Mix in some charcoal, or do a charcoal swirl.

The benefits of charcoal in soap include being fantastic for acne and great at purifying in warmer climates, as well as being a good additive to prevent your fragrance disappearing before you ever get to use your soap! However, charcoal is a black powder and it will change the colour of your soap. Doing a swirl with charcoal is another option, so part of the soap is more fragrant, which will improve the overall effect while still letting you use nice colours in the rest of the soap.

That’s my 10 ways to fix your soap if your essential oil fragrance is too faint or if your essential oil fragrance doesn’t last. Do you have any other ways? Share them in the comments!