It’s summertime, and for many of us that means spending a lot of time outside — and, unfortunately, because of mosquitoes.
The combination of increased temperatures and abundant water is ideal for these blood-sucking insects to make their presence felt.
At best, they are an insect, delivering an extremely unpleasant sting. At the other end of the spectrum, they are carriers of diseases responsible for more human deaths than any other animal on Earth.
To keep them away, many of us will reach for a bottle of insect repellent or citronella candles to avoid bites and the constant itching that comes with them. But how do these repellents actually work?
a complex interaction
A lot of research has been done to understand how and why female mosquitoes – the ones that bite us – are attracted to people.
There is evidence that they are attracted to the carbon dioxide we exhale, the lactic acid found in our sweat, and many other skin odors and volatile compounds we exhale. The interplay between all these factors is quite complex.
Physical barriers such as nets provide the best protection against mosquitoes. However, while you can place traps around backyard patios and barbecues, it is not practical to do so for any larger space.
This is where repellents come in.
deterrent
There are different types of mosquito repellents available.
The most tried-and-true products are based on a substance called N,N-diethyl-meta-toluamide, commonly known as DEET.
This molecule has been commercially available since 1957, when the United States military discovered that it was an effective insect repellent.
DEET is often used as a point of comparison for studies examining alternatives. Studies show that, provided they are used as directed, DEET products are safe and effective.
For example, it is recommended that sunscreen be applied before repellent, when necessary. DEET products are not recommended for infants.
The exact mechanism by which DEET repels mosquitoes and other insects is still being discovered.
Many studies link its success to mosquitoes’ receptors sensing the presence of DEET, which prevents them from coming close to our skin. Some investigations show that when DEET is detected, it blocks the attraction of mosquitoes to us, while other evidence shows that mosquitoes “smell and avoid” DEET.
There are also several reports showing that mosquitoes do not bite when they come across DEET-treated skin. This is because DEET acts as a contact-based repellent and delivers a chemical message to mosquitoes to leave. Studies suggest that DEET probably works through a combination of the processes described here.
effective option
A more recent family of mosquito repellent products relies on an active ingredient called picaridin (or icaridin).
The current consensus is that picaridin products are safe and highly effective. For many people, they are considered attractive because they do not have as strong a smell as DEET.
Picaridin products have been reported to be just as effective as DEET, or in some cases, even slightly better, although results also depend on their concentration.
Another repellent routinely reported to be effective is para-menthane-3,8-diol (PMD).
It is produced by chemical treatment of lemon eucalyptus oil.
Untreated, this oil is not effective in repelling mosquitoes. However, several studies have shown that PMD is an effective mosquito repellent.
The ability of these repellents to deter mosquitoes is dose dependent.
In all cases, it is important that an appropriate dose is applied, with occasional re-application required to maintain maximum protection. The performance of these products also varies according to many other factors, including the species of mosquitoes.
What about citronella?
Citronella products, including candles and topical formulations, are popular choices for keeping mosquitoes away.
However, in systematic testing, these have been shown to be much less effective than DEET.
Studies have also shown that citronella candles do not protect against mosquitoes as much as you would like.
There are many other repellent products on the market.
Given the widespread interest in preventing mosquito bites, natural remedies are available in abundance. It is important to recognize that natural is not necessarily more effective and it is not necessarily safer.
In most reported studies, DEET and picaridin have been reported to have the greatest duration of protection (on the order of hours) and the greatest effect on mosquitoes. They are tested more thoroughly than many alternatives.
When others are tested, they are often found deficient.
One study described sound-based devices as being as resistant to snake oil. And although repellent bracelets contain working ingredients, they are largely ineffective in that form. This is due to insufficient concentration of the active ingredient being “emitted”.
When it comes to preventing disease transmission through mosquitoes, the benefits of proven repellents far outweigh the risks.
(Author: Daniel Aldridge, Senior Lecturer in Chemistry, Swinburne University of Technology)
(Disclosure statement: Daniel Aldridge does not work for, consult for, own shares in, or receive funding from any company or organization that would benefit from this article, and he has no affiliations beyond his academic appointment.) Have also not disclosed relevant affiliations.)
This article is republished from The Conversation under a Creative Commons license. Read the original article.
