In the summer months, mosquitoes are a real nuisance for vacationers. Although mostly harmless, they can sometimes be deadly. They are believed to have killed more people than any other insect or animal by transmitting diseases such as Zika, dengue fever, and malaria. Every year they kill nearly three million people worldwide. Why do they bite us? How can we prevent them? How can we treat the bites?
Why do we get bitten by a mosquito?
In mosquitoes, it is the female that is responsible for human bites. After mating, the female mosquito looks to mammals for blood to provide a source of protein to feed her eggs.
Forty-eight hours after taking this food, the fertilized females lay their eggs on the surface of stagnant water (ponds, streams, marshes, etc.). This sequence of breeding, biting, and spawning is repeated several times during the life of the mosquito. The length and frequency of the cycle depend on the species, but it is estimated that the common mosquito repeats this cycle twice a week in summer. A single bite is more than enough to satisfy the protein requirements of the eggs, so it is not true that a single mosquito can be responsible for several bites in one night. The bite is usually nocturnal (usually at dawn or dusk) and painless, lasting about three minutes if the mosquito is not disturbed.
NB: It is not necessary to turn off the light to avoid them; the mosquito finds its target by smell. First of all, it can smell carbon dioxide (emitted by breathing and sweating of living things) at a distance of more than thirty meters. The closer it gets, the more it detects a human odor, composed of fatty acids (fatty acids, butyric acid), lactic acids, or other ammonia odors secreted by the skin, such as breath or urine. In proximity to human skin, it uses thermoreceptors. These infrared heat sensors allow them to locate the warmest veins from which they draw the blood they need to feed their eggs. The visual system, which is mainly sensitive to movement, is actually very inefficient.
Why do mosquito bites itch?
Once the mosquito is on the spot, it pushes its needle through the skin into a human vein. Through the first channel, formed by the hypopharynx, it injects saliva, which prevents blood from clotting. The second channel allows it to suck out the liquid blood. The amount of blood collected varies from 5 to 10 mm3. When the mosquito has finished its meal, it leaves as it came: without worrying about what is happening inside the human body.
The saliva, which was only intended to stabilize platelets, has a completely different effect. When confronted with this unknown substance, our immune system goes into alarm and sends mast cells to the forefront. These cells have the ability to detect foreign substances and burst on contact to protect the body. When they burst, they release large amounts of histamine, which causes familiar redness and itching. Other agents of the immune system are then attracted and a small red pimple forms. This is a water-filled swelling of the skin: under no circumstances should you try to prick it or you risk infection.
This explains why bites tend to itch much more in spring than in late summer when the body is getting used to the mosquito’s saliva.
Why does scratching give us relief?
It is often said: mosquito bites should not be scratched. Easier said than done… But why does it feel so good to scratch?
To understand this phenomenon, we have to look at what happens in the skin when a bite occurs. We know that the skin has many sensors that can interpret external stimuli. These sensors are connected to sensory fibers that indicate to the brain that the body is in danger: burns, cuts, pinches, etc. This is warning information. For example, if the skin is burned, the brain generates a sensation of pain to warn the person of danger. In the case of mosquito bites, sensory fibers transmit the detected inflammation and the brain triggers itching.
Some sensory fibers are able to perceive simple tactile signals, such as caresses. These stimuli do not send signals to the brain, but they do carry contact information. Contact information and alert information travel in the same neural network when they are in close proximity. There can be an interaction between the two and one information can parasitize the other.
So when we scratch around a mosquito bite, the brain perceives the contact information and we short-circuit the alert information. In a short time, the brain stops receiving the message of inflammation and the itching disappears. This reduction of pain perception can also be illustrated when we receive a hit and massage the injured area. The same mechanisms are at work.
However, one should avoid succumbing to the temptation as much as possible. Scratching can allow bacteria to penetrate the skin and cause superinfections. And the more you scratch, the more it itches. How can this phenomenon be explained?
In fact, the mechanical action of scratching activates nerve endings and releases histamine molecules, which in turn cause itching. It is a vicious circle.
As we have seen, the itching is caused by an allergic reaction to the mosquito’s saliva. Some organisms, for unknown reasons, do not consider it harmful and the allergic reaction goes virtually unnoticed. So, they feel less bitten than others!
Favorite body odors
Mosquitoes are attracted to the pheromones we release, some of which are more attractive than others. This can be related to diet, levels of sweating, use of perfumes, or the bacterial composition of our skin.
It should also be noted that pregnant women tend to be stung more often because they secrete a lot of hormones.
Tips to combat mosquitoes, treat bites, and prevent mosquito bites
Adopt good personal hygiene
As mosquitoes are attracted by body odor (grease, sweat), it is important to follow good personal hygiene. Some odors may attract mosquitoes, while others repel them, so there is no simple rule about odors.
Keep skin covered
Clothing can also be important. The longer and looser the clothing, the less skin exposure. Another option is to wear socks. But this advice is often difficult to follow in the summer heat. Remember that it is recommended to wear light-colored clothing, as mosquitoes are attracted to dark colors, which radiate more heat.
Avoid places near standing water
Mosquitoes gather near places where they can lay their eggs. Therefore, try to eliminate stagnant water (buckets, waste garbage cans, tires, containers…), and cover water tanks.
Use a fan
On windy days, bites are less likely because mosquitoes cannot fight against the air current. Placing a low-speed fan 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 outdoors without protection at this time.
Use a mosquito net
A mosquito net is essential if you want to sleep without the buzz of mosquitoes. If impregnated with insecticide, it is an excellent preventive measure.
Use a repellent
Permethrin-based repellents can be used on clothing. However, it is important to remember that permethrin is toxic to cats and many amphibians.
There are products that can be applied to the skin to prevent mosquitoes from approaching and biting: these are called repellents. Health authorities have unanimously recognized four molecules with anti-mosquito activity: DEET (the best known), KBR (or picaridin), IR 35/35 (recommended for pregnant women), and citriodiol.
These substances block the mosquitoes’ olfactory receptors. Because of their effectiveness, they are best used only in special situations, i.e. when there are many mosquitoes and there is a risk of disease transmission. In other circumstances, it is usually sufficient to follow a series of practical tips.
Does citronella work?
Although the insect usually avoids the plant, it is not enough to keep them away if they need blood. If you like the smell of citronella, you can use candles or scents, but the effect is very small.
Insecticide sprays and diffusers are only useful if the room is closed. They can pose a health risk to humans (especially children) and contribute to mosquito resistance to insecticides: they should therefore be used sparingly.
Caution with traps
Different studies have also shown that blue bulbs are not effective: only 0.2% of the insects captured by these bulbs are mosquitoes. In addition, they are harmful to the environment because they kill insects that are beneficial to ecosystems.
Tips on how to relieve mosquito bites
Antihistamines: The use of antihistamines is very effective. As a cream, they act by blocking the effects of histamine and relieving the most intense itching. The effects of antihistamines begin to take effect within an hour of use.
Corticosteroids: Corticosteroids are often very convenient and effective against itching. They reduce the effects of the inflammatory reaction, i.e. both itching and swelling. If used in the morning and evening, the itching decreases in two to three days. The only problem is that sometimes a prescription is needed to obtain these creams.
Washing with soap: Wash the affected area with soap and water.
Apply heat: There is nothing better than heat to reduce itching. Apply heat on the itching area (cloth soaked in hot water, lamp, coffee cup) for about fifteen seconds. Conversely, an ice cube can be just as effective.