Table of contents:
- What happens in your body when you are bitten by a mosquito
- Why do mosquito bites itch?
- Why does scratching an itch feel good?
It seems that we are all familiar with the following scenario: In the middle of a deep sleep after a stressful day of work, you hear a disturbing hum and suddenly feel a sharp sting in your hand or leg. Not long after, a red rash appeared on the skin.
Without thinking, you instinctively start scratching. Your skin turns red, the mosquito bite marks get itchier more and more, and you wake up from the dream only to find two new reddish bumps from another mosquito bite. After a long night of sweet dreams, I was replaced by the busyness of driving away the stubborn mosquitoes and at the same time scratching the itch that never stopped.
What happens in your body when you are bitten by a mosquito
A mosquito doesn't bite. The female mosquito uses its needle-like mouth to stab into the skin of its prey, which it then uses to suck blood.
Less than five percent of skin is blood vessels. So, when a mosquito lands on you to find food, it has to 'fish'. From afar, the mosquito's muzzle may look like a thin needle, but in fact this muzzle - called a proboscis - is a sawing and suction set, enclosed in a tube called the labium. When going to suck blood, the tube will open and reveal the six parts of the mouth (filaments) that pierce into the skin.
When "biting" its prey, these six parts of the mouth will expand and move flexibly to find the nearest blood vessel. Often, this process ended in several search attempts, and took several minutes, to successfully harvest blood.
The mosquito will then move four filaments to work like saws and jacks to help expedite the blood-sucking process by two parallel tubes - the hypopharix, which releases saliva into the skin, and the labrum, which sucks blood.
The mosquito will suck so hard that the blood vessels start to buckle. Some may burst, shedding blood in the surrounding area. When this happens, the mosquito will usually 'add', drinking blood directly from the pool of blood it has created. The saliva that is released contains anti-coagulant agents that keep the blood from clotting so that mosquitoes can easily suck the blood.
Why do mosquito bites itch?
Itching and bumps from mosquito bites are caused not from mosquito bites or mosquito saliva, but the response of the body's immune system to the saliva. Mosquito saliva contains high levels of enzymes and proteins that bypass your body's natural blood clotting system. This anticoagulant directly causes a mild allergic reaction in your body.
The human immune system responds to these allergens by releasing histamine. Histamine causes the blood vessels around the mosquito bite area to become inflamed, causing red bumps on the skin. Histamine also irritates the nerve endings in the skin and causes itching.
Why does scratching an itch feel good?
Scratching is a relatively minor form of pain. When we scratch, this movement blocks the itching sensation of the accompanying pain, temporarily distracting the brain from the itching sensation; it's the same with applying cold, or hot compresses, or even a little electric shock.
These pain signals are sent to the brain by bundles of nerves just as sensations of itching are sent by different bundles of nerves.
When we are faced with a potential danger, the body responds with a withdrawal reflex. Just try to put your hands over the fire, it won't be long before you will have a great desire to immediately pull your hands away from the heat. However, scratching brings reflex closer to the problem skin. It makes sense, because closer inspection and brief scratches are more effective at getting rid of crawling insects on your body than away from them.
Scratching is a great way to not only get rid of insects and parasites, but also plant residue and other foreign objects that have stuck to your skin.
In addition, your brain rates itching scratching as an act of reward, the sort of reward you "deserve" after dealing with pain or stress - from a mosquito bite - by releasing dopamine throughout the brain. Dopamine is a neurotransmitter in the brain that regulates movement, emotions, motivation, and feelings of pleasure. When activated, this system will reward our behavior and make us happy, which triggers us to do it again and again for the same satisfaction.
