Pimples, redness, itching... In summer, mosquitoes are a real nuisance for holidaymakers. Although they are mostly harmless, they can sometimes be deadly. They are considered to have killed more people than any other insect or animal through the transmission of diseases such as dengue fever or malaria.
Every year they kill nearly three million people worldwide.
Why do they bite us? How can we stop them? How do we relieve a bite?
Feeding your eggs
As with wasps and bees, female mosquitoes are responsible for human bites.
After mating, the female goes hunting to collect mammalian blood to find the protein source needed to feed her eggs.
Forty-eight hours after taking this meal, the fertilized females deposit their eggs on the surface of stagnant water (ponds, streams, puddles...). Water is absolutely necessary for the development of the mosquito's eggs: a wetland will not suffice.
This "reproduction-biting-bitten-bridge" sequence is repeated several times during the mosquito's life. The length and frequency of the cycle depend on the species, but it is estimated that the common mosquito reproduces this cycle twice a week in summer.
One bite is more than enough to cover the protein needs of the eggs, so it is not true that one mosquito can be responsible for several bites in a single night. The bite, which is usually nocturnal (usually at dawn or dusk) and painless, lasts about three minutes if the mosquito is not disturbed.
Spotting your prey
No need to turn off the light to avoid them, the mosquito locates its target through its sense of smell.
It is first able to sense the presence of carbon dioxide (emitted by the breathing and perspiration of living beings) at a distance of more than thirty metres.
The closer it gets, the more it will detect human odours composed of fatty acids (sebum, butyric acid), lactic acid or other ammoniated odours emitted by the skin, such as breath or urine.
When it is very close to human skin, it uses thermoreceptors. These infrared heat detectors will enable him to find the warmer venule, inside which he will draw the blood necessary for his egg-laying. The visual system, which is especially sensitive to movement, is in fact very inefficient.
Why does the mosquito bite itch?
How does a bite happen?
When the mosquito is in place, it pushes its stylets through the skin into the human vein.
Through a first channel, formed by the hypopharynx, it injects saliva that prevents blood from clotting in its tube. The second channel allows him to suck out the blood that has remained fluid.
The amount of blood drawn varies from 5 to 10 mm3. When the mosquito has finished its meal, it leaves as it came: without worrying about what is happening in the human body.
The immune system on alert
So the mosquito did not disperse an anaesthetic into the body, as is often said.
Its saliva, which was only intended to stabilize blood platelets, will have a completely different effect. Faced with the presence of this unknown substance, our immune system goes on alert and sends mast cells to the front line. These cells have the ability to detect foreign substances and explode on contact with them to protect the body.
When they explode, they release massive amounts of histamine, which causes the redness and itching we know. Other immune agents are then attracted and a small red pimple appears.
This is a swelling of the water-filled skin: under no circumstances should you try to pierce it, as this could lead to infection.
This explains why the bites usually itch much more in the spring than in late summer when the body has gradually become accustomed to the mosquito's saliva.
Why does scratching make us feel better?
We often say it often enough: we should not scratch our mosquito bites. Easier said than done... But why does scratching do so much good?
Two types of sensors
To understand this phenomenon, you need to observe what happens to the skin during a sting. It is known that the skin has many sensors capable of interpreting external stimuli.
These sensors are connected to sensory fibres that will transmit to the brain the information that the body is in danger: burn, cut, pinch... This is warning information.
For example, when the skin is burned, the brain induces the perception of pain to alert the individual to the danger he or she is in. Here, in the case of a mosquito bite, the sensory fibres transmit the inflammation they have detected and the brain induces itching.
Some sensory fibres are able to perceive simple touch signals, such as caresses, for example. These stimuli will not alert the brain, but they still carry information called contact information.
The contact information and the alert information will circulate within the same nervous network if they are located in a nearby area.
Interactions can take place between the two, and one piece of information can interfere with another.
So when we scratch around a mosquito button, the contact information is perceived by the brain and we short circuit the alert information. For a short period of time, the brain no longer receives the message of inflammation and the itching disappears.
This reduction in pain perception can also be seen when we take a blow and massage the injured area. The same mechanisms come into play.
The more it itches, the more I scratch myself
However, we must avoid succumbing to temptation as much as possible. Scratching can allow bacteria to pass through the skin and cause superinfections. And the more you scratch, the more it itches! How do you explain this phenomenon?
In fact, the mechanical action of scratching activates nerve endings and will release histamine molecules, which in turn will cause itching. It's a real vicious circle.
Who gets bitten the most?
Contrary to popular belief, mosquitoes are not sensitive to the amount of sugar in their blood. So "sweet skins" can be reassured! In reality, there are two main reasons for this phenomenon.
As we have seen, the itching is due to an allergic reaction to the mosquito's saliva. Some organisms, for unknown reasons, do not consider it harmful and the allergic reaction goes almost unnoticed. They will then feel as if they are less stung than others!
Favorite body odors
But recent research shows that this is probably not the only reason. Mosquitoes are attracted to the body odor of organisms. These are linked to the pheromones we give off, some of which are more attractive than others.
This can be related to food, the amount of sweat, the use of perfume but also to the bacterial composition of our skin.
It is this last point that has caught the attention of researchers at the University of Wageningen (Netherlands). They studied 48 men to try to find out which smells and which bacterial populations were preferred by mosquitoes.
Nine of them were particularly bitten, while seven managed to get through the net. Among those who were the most bitten, the same characteristic is often found: a large number of bacteria.
We find in the very attractive bacteria that emit powerful volatile compounds: Leptotrichia sp., Delfia sp., and Actinobacteria Gp3 sp.
On the other hand, the carriers of Variovorax sp. and Pseudomonas sp. are only slightly bitten...
It should also be added that pregnant women are generally pricked more because of the hormones that are abundantly secreted.
Anti-mosquito tips for treating a bite and avoiding being bitten
Adopt good personal hygiene
Since mosquitoes are attracted by body odors (sebum, sweat), it is important to adopt good personal hygiene. Some perfumes can attract females, others repel them, so there is no specific rule regarding fragrances.
Expose the skin to at least
The way you dress can also make a difference. The longer and looser the clothes are, the less skin is exposed. You may also consider wearing socks.
But this advice is often difficult to follow because of the heat in the summer. Just remember to wear light-colored clothing because mosquitoes are attracted to darker colors that emit more heat!
Avoid places near stagnant water
Mosquitoes are numerous near the places where they can lay their eggs. Therefore, try to eliminate stagnant water (buckets, garbage cans, tires, containers ...), cover water tanks, drain water from tarpaulins ...
Place a fan near you
There are fewer bites on very windy days because the mosquitoes cannot control the airflow. Placing a fan at low speed on the balcony or in the bedroom will prevent them from entering or moving around properly.
Protect yourself, especially at the end of the day
Mosquitoes are most active at the end of the day. Avoid being outside without protection during this period.
Adopt the mosquito net
To make sure you sleep without being woken up by the buzzing of mosquitoes, you need a mosquito net. If it is treated with insecticide, it is the prevention of choice.
Use a repellent
For clothing, permethrin-based repellents can be used. They are resistant to several items of washing and are very effective.
However, it must be kept in mind that permethrin is toxic to cats.
There are products that are applied to the skin and that prevent the mosquito from approaching and biting: these are repellents.
Four molecules have been unanimously recognized by health authorities for their mosquito repellent power: DEET (the best known), KBR (or picaridin), IR 35/35 (recommended for pregnant women), and estradiol.
These agents block mosquitoes' olfactory receptors. Because they are potent, it is best to reserve them for certain specific circumstances, i.e. where there are large numbers of mosquitoes and where there is a risk of disease transmission. For other circumstances, it is usually sufficient to follow a number of practical tips.
Does citronella work?
Although the insect generally avoids this plant, it is not enough to stop it when it needs blood.
If you like the smell of lemongrass, you can use candles or essences, but you should know that the impact is very low.
As for insecticide aerosols and diffusers, they are only of interest when the room is closed. They can present a risk to human health (children in particular) and contribute to the resistance of mosquitoes to insecticides: they should, therefore, be used with great moderation.
Beware of traps
A report from the French Society of Parasitology listed mosquito repellents to avoid: "It is strongly recommended not to use insect repellent wristbands to protect against mosquitoes, ultrasound sound devices, vitamin B1, homeopathy, electric snowshoes, ribbons, paper, and other sticky stickers without insecticides. »
Similarly, university studies have shown that blue light lamps are not effective: only 0.2% of the insects trapped by these lamps are mosquitoes.
Moreover, by killing insects that are beneficial to ecosystems, they would be harmful to the environment.
Today, the ANSM (the French National Agency for the Safety of Medicines and Health Products) is trying to regulate this market and monitor products to check whether they are active against mosquitoes and whether they are not toxic to humans.
How to relieve a mosquito bite?
The damage is done: a small red pimple has appeared and the itching is more intense. Here are 6 tips to relieve them... Here are our tips to relieve a mosquito bite.
Washing with soap
Wash affected area with soap and water. Marseille soap has a calming effect (rub in the area of the bite).
Use baking soda
The use of baking soda (also called "little cow") is an interesting possibility. Mix baking soda (3/4) with water (1/4) and soak a cloth in this solution. Then apply the cloth to the mosquito bite.
Medicinal or aromatic plant leaves provide relief when rubbed on the pricked area. Take one or two leaves of plantain (a common weed), knead it between your fingers (to obtain juices), and rub generously over the bite. Also use dandelion leaves, mint leaves, onion rings.
Apply a heat source
There's nothing like heat to parasitize the itching! Apply a heat source in the close vicinity of the bite site (cloth soaked in hot water, lamp, a cup of coffee) for about 15 seconds. Conversely, an ice cube can be just as effective.
The use of antihistamines is very effective. In cream form, they act by blocking the effects of histamine and relieve even the most severe itching. The effects of antihistamines (Benadryl, Reaction) begin to be felt within an hour of use.
Corticosteroids are generally very comfortable and very effective against stings. They reduce the consequences of the inflammatory reaction, i.e. both the itching and swelling of edema.
The application in the morning and evening makes it possible to reabsorb the sting in two or three days. The only catch: a prescription is sometimes required to obtain these creams.