Roaches are top of the list of household pests you don’t want in your home! And what’s more they’re notoriously tough critters. Once installed, they can be hard to get rid of.
That’s where creative approaches to pest control can be a lifesaver. And smells are a great way to get unwanted trespassers to leave of their own accord – or even better, stay away in the first place.
But what smells do roaches hate? Well, look online, and you’ll find a whole host of home remedies being touted as roach deterrents. Here we take a look at the scientific evidence behind the claims.
What Smell Do Roaches Hate?
Most of us are familiar with oregano as an herb in Italian cooking. But oregano essential oil is also an extremely effective roach repellent. And there’s scientific evidence to prove it!
Scientists mixed the oil with acetone to test if it deterred brown cockroaches. The results were impressive. Almost all the roaches in the experiment – 99 per cent – steered well clear of the mixture. And they were still staying away a week later.
Interestingly, the strongest repellent effect was observed with the weakest concentration of oregano oil – 2.5 parts per 100. When the concentration was increased to 30 parts per 100, the repellent effect fell to 96.5 per cent. Still impressive, but not as good as the weaker mixture.
That might make you wonder whether, in fact, it was the oregano oil or the acetone that was repelling the roaches.
But oregano mixed with acetone was also put to the test as a poison. Several different strengths were tried out, ranging from 2.5 to 30 parts of oregano oil per 100 parts. When it came into contact with roaches, all but the weakest mixture killed them all.
With the weakest solution, only 62 roaches per 100 died. That suggests that it’s the oregano oil that’s doing the damage, not the acetone.
All this means that oregano oil is a great option to deter roaches from your home. And if any critters do get in, they won’t last long if they touch it.
Acetone, of course, isn’t the most pleasant of chemicals. But spraying neat essential oil around your home isn’t practical. And judging by the results of these experiments, it probably isn’t the most effective approach either.
A good alternative is distilled water. Add a few drops of essential oil to a spray bottle, fill it with water, then spray liberally wherever you suspect roaches are hiding.
The same study that found oregano oil was an effective roach deterrent also gave a big thumbs up to another herb – rosemary.
Of all the essential oils tested by the scientists, rosemary was the most toxic to brown cockroaches. If they came into contact with it, they died. All of them. The result was the same whether the mixture contained 30 parts of rosemary oil per hundred, or just 2.5 parts.
It works just as well if you want to stop cockroaches ever getting into your home in the first place. And as with the oregano oil, lower concentrations actually work best. In the study, the mixture of 2.5 parts rosemary oil was the most effective, with a repellency effect of just over 94%.
Mint is another essential oil that can act as both a deterrent and a poison to roaches. And there’s good scientific research to back up its credentials.
Scientists have found that mint oil effectively repels at least three different kinds of roaches – brown, American, and German.
One experiment gave roaches a choice of two boxes to walk into, one with peppermint oil and the other without. In every case, the roaches steered clear of the box with the peppermint oil.
And just as with oregano oil, mint oil is toxic to roaches if they come into contact with it. That’s the case whether it’s placed directly on their bodies or comes into contact with them through fumigation.
Prevention is always better than cure. So placing some peppermint oil around doors and window frames is an easy way to help avoid roaches crossing your threshold. And there’s the added bonus that it will make your home smell lovely too.
The strong, clean scent of eucalyptus will be familiar to anyone who’s ever had a cold. That’s because it’s often used as an herbal remedy to clear noses and sinuses. But this useful plant is also an effective roach deterrent.
While eucalyptus oil helps us breathe when we have a cold, it seems to have the opposite effect on roaches. One study found that its presence reduced the amount of oxygen American cockroaches could breathe in. And that meant they avoided it like the plague.
Other studies have shown that soybean oil is a very effective carrier for the eucalyptus oil. Mix the two together, and you’ll have a very effective roach deterrent.
The combination was found to successfully repel over 80 per cent roaches for the first hour after application. And almost two thirds of roaches were still being repelled 48 hours later.
Concentrate the mixture in places where you suspect the roaches are hiding out. And reapply it every couple of days to ensure the repellent effect continues to be effective.
The sharp, zingy scent of citrus fruit might be appealing to humans, but roaches respond to it quite differently!
Different citrus oils have different chemical compositions. But they all contain a compound called limonene. This effectively repels a number of insects, including roaches.
One study looked at no fewer than 17 different essential oils to see how well they repelled the German cockroach. It found that four of the five most effective oils were citrus-based – grapefruit, lime, lemon, and orange.
What’s more, those oils were effective against American and smoky-brown cockroaches too.
They can be used neat – wipe some onto a paper towel and apply to doorways, windows and any other potential entry points. Alternatively, you can add a few drops to water in a spray bottle. Then shake it up and spray the mixture wherever you think roaches are getting in and hiding.
We’ve already seen that a number of herbs are good cockroach deterrents. And we know that a lot of citrus fruits work well too. So perhaps it’s not surprising that lemongrass – a citrussy Asian herb – is also great at getting rid of roaches.
A 2018 study found that lemongrass essential oil was lethal to German cockroaches when it came into contact with them.
And at lower concentrations, it was incredibly effective as a deterrent. In fact, it scored a perfect 100% repellency rating. And its effect was just as strong throughout the 48 hours of the trial period.
Lemongrass essential oil is regularly used in aromatherapy, reputedly reducing stress, anxiety, and depression. That means it’s readily available online. And whatever its therapeutic properties, getting shot of a roach infestation is bound to improve your stress levels!
We all know that cats love catnip – but it turns out that roaches hate it!
A study by Iowa State University looked at whether catnip oil could be used to repel German cockroaches. And the answer was a resounding yes.
Catnip essential oil was actually more effective against roaches than the same concentration of industrial pesticide DEET. The study found this was the result of two compounds of a chemical called nepetalactone.
There are plenty of catnip sprays and oils on the market. Or if you prefer, you could make your own. The best approach is steam distillation, for which you’ll need special equipment. If you already have experience distilling, this could be a good option.
But if not, an alternative is to infuse olive oil with catnip. You can do that by chopping up the herb, placing it in a casserole dish with the olive oil, and gently heating it in the oven for two to three hours.
One thing for cat owners to be aware of is that some commercially available catnip oils are very strong. The type used for aromatherapy for humans will be great for seeing off roaches. But it’s far too pungent for kitties, and should be kept well away from feline friends.
One smell that doesn’t deter roaches
Lavender smells lovely. It’s often used to help people relax and sleep. And if you search online for smells roaches apparently dislike, it crops up time and time again.
But while it can repel some smaller insects – fleas and flies, for example – there’s no scientific evidence that it works for roaches.
So keep this one for your bedside oil burner.
Smells that roaches hate: a quickfire summary
Essential oils can be a very effective – and natural – way to deter roaches. But it’s important to choose the right ones!
So what smell do roaches hate? Oregano, rosemary, mint, eucalyptus, lemongrass and catnip are great herby options. Citrus oils work brilliantly too. And surprisingly, lower concentrations – 2.5 parts per hundred – seem to work best as deterrents.
Just don’t bother with lavender. Its sweet fragrance is beautifully relaxing – but it doesn’t appear to have any effect on those pesky roaches.