As summer begins, many parents take advantage of the weekend to take their children to the countryside for hiking, stream tracing, and lychee picking. They thought that wearing long sleeves (sun protective clothing or ice sleeves) and long pants would keep away insects, but their arms and legs were still bitten, red and swollen, and the itching was unbearable.
With the summer vacation approaching, parents who plan to send their children to summer camps or back to the countryside must not forget to prepare for insect repellent. In this issue, let’s talk about – why can mosquitoes bite people through clothing? And how to prevent it?
How do mosquitoes locate humans?
Many people think that mosquitoes find people by “smelling blood”, such as believing that certain blood types are more attractive to mosquitoes, which is actually a misconception.
In fact, mosquitoes are mainly driven by the following “human signals” [1]:
-
Drawn by “news”:
Mosquitoes at rest are first activated by the chemical signals emitted by humans, such as carbon dioxide, skin odor (including volatile components such as lactic acid, ammonia, etc.)
and under the guidance of these signals, they seek hosts. -
Landing preparation:
When mosquitoes fly less than 1 meter away from the human body, they hover around, “detecting” human odors, body temperature, humidity and other information to determine the appropriate “landing point”.
Image source: Reference [2]
Summer clothing often uses fabrics that are highly breathable and easy to dissipate heat. The thickness of these fabrics is small, and the gaps are large, human sweat, odor, and heat can quickly volatilize through the fabric gaps,mosquitoes track these signals and approach to “bite”[2].
Image source: Reference [2]
In addition, being easily bitten by mosquitoes in summer is also related to their reproductive cycle.
High temperature and humidity significantly accelerate the reproduction of mosquitoes
—the development cycle from “eggs” to “adults” can be shortened from 2 weeks to 4 days, which speeds up the reproduction rhythm of mosquitoes[3]. Mosquitoes need enough protein and other nutrients to lay eggs, so they need to feed on blood.
Why can mosquitoes bite through fabric?
1. Strong penetration ability
Mosquitoes not only have an accurate tracking system, but also complex and lightweight mouthparts, which can easily penetrate the skin and hardly cause pain when biting (most of the pain and itching we feel is due to an allergic reaction to mosquito saliva). In medical research, when optimizing microneedle devices for subcutaneous drug delivery, the structure of mosquito mouthparts has also been referenced. [4]
Mosquito mouthparts
This seemingly single “needle” mouthpart is actually composed of multiple components, let’s focus on these two groups[4]:
-
Labrum needle（labrum, gray area in the figure below）: This is a hollow fine needle,
responsible for blood sucking. -
Maxilla needle（Maxilla, yellow area in the figure below）: This is a pair of fine serrated long needles, covered outside the blood-sucking duct, responsible for “sawing” open the skin.
Image source: Reference [4]
2. The mouthparts are very thin
Image source: Reference [4]
Figure a, “Labrum needle”（labrumm）diameter less than 50 microns; Figure b, “Maxilla needle”（Maxilla） diameter less than 10 microns [4].
If the thickness of the clothing fabric is less than the length of the mosquito’s mouthparts, or the fabric gaps are large, mosquitoes can easily penetrate.
Taking common pure cotton clothing as an example, research on 100% pure cotton plain fabric samples found that the measured pore size range of different commercial plain fabrics is 46–344 microns[5]. Although there are differences in the diameter of the mouthparts of different mosquitoes, penetrating gaps of more than 100 microns is more than enough.
In addition, tight-fitting clothing(such as ice sleeves) when stretched, the fabric gaps are enlarged, making it easier for mosquitoes to attack.
Therefore, some researchers are developing mosquito-proof clothing from the “fabric structure”, by increasing thickness and reducing gaps, making it impossible for mosquitoes to reach the skin. [2] But the related products have not yet been commercialized.
Three approaches to mosquito-proof fabrics. The circle represents the head of a mosquito, the black line below the circle is the mouthparts, and the side black line is the detector (i.e., chemical receptors); blue represents fabric, and beige represents skin. Image source: Reference [2]
When long sleeves and long pants can’t help,
how to effectively repel mosquitoes?
We can indeed repel mosquitoes by increasing the thickness of clothing and sacrificing breathability, but in summer, dressing like this is not only uncomfortable but also increases the risk of heatstroke.
One measure that many friends may not have tried is to use –clothing mosquito repellents, such as pyrethroid compounds.
These repellents are used on clothing and other fabrics, and they last much longer than skin repellents and are resistant to washing.
The World Health Organization（WHO）‘s 2019 World Malaria Report shows that between 2000 and 2015, approximately 663 million cases of malaria were averted globally through malaria control measures, of which 68% of the success is attributed to the large-scale promotion of “long-lasting insecticidal nets”（Long-Lasting Insecticidal Nets）.
These nets are pre-treated with pyrethroid compounds, and the repellent effect can last for several years. In addition, protective measures such as curtains, clothing, etc., treated with long-lasting insect repellents, also have a significant effect on blocking vector-borne diseases such as malaria.
[2]
The principle of these repellents is also —— interfering with mosquito olfactory receptors,
making it difficult for them to track humans. But the difference is that long-lasting repellents
can continuously release effective ingredients and have a certain resistance to washing, thus extending the protection time.
Taking “Sawyer (Sawyer) 0.5% permethrin clothing mosquito spray” as an example, after the spray dries, the repellent effect can last for 42 days, or withstand 6 washes, suitable for clothing, socks, mosquito nets, screens, sheets, tents, etc.
The illustration is AI-generated and for reference only
These fabric mosquito repellents can be used as a supplement to skin mosquito repellents. If you are worried about increasing the burden of luggage, you can spray before going out
. Especially suitable for:
- Going hiking in summer, or playing water sports such as kayaking, sweating or getting wet, the effect of skin mosquito repellents will decrease（need to re-spray / re-apply）. But if you wear clothes treated with permethrin, it can also provide protection at this time.
- Summer vacation, children participating in summer camps, study tours and other group activities alone, after bathing not using skin mosquito repellents in time, the permethrin on the clothes can still provide protection.
For children returning to the countryside for the summer vacation, you can bring a bottle directly,mosquito nets, sheets, curtainscan all be sprayed. In addition, permethrin is more effective against ticks than other common mosquito repellents(such as DEET, picaridin), ticks are more common in grassy, shrubby areas.
References
