I couldn’t leave it alone. I started thinking about mosquitoes, mosquito bites, and my swollen, itchy self. Since I’m a medical student the next thing I know I’m thinking about immune reactions, what was happening under my skin as I was swelling, the wheal and flare, and so on.
So here we go–
First you get a bite. I just learned that only female mosquitoes do the biting. If you want to be technical about it, she sticks her proboscis into your skin, releases anticoagulants with her saliva, and sucks your blood into her tummy. Her saliva remains behind, and this is what causes the body to react.
Your body reacts to the proteins (of which there are about 20 in the adult) in the mosquito saliva. Generally the bite turns red, swells, and itches like hell.
Your body knows that it has been invaded by a foreign substance, so what it wants to do is send its troops to the site of the invasion to fight off, in this case, the foreign mosquito saliva proteins. (Almost as exciting as all the zombie fighting going on at Pax Arcana). The troops (the white blood cells/leukocytes) travel through the blood stream, so the best way to promote this is to dilate the blood vessels. Once they get where they need to be, they need to get out of the blood vessel and into the tissue. This is why our capillaries become permeable. In other words, blood will flow to the site of the bite and then the leukocytes will move through the capillaries and into the tissues, which allows them to fight-off and break down the intruding proteins. Thus we have redness and swelling. Vasodilation and blood to the site of the bite (redness and heat) and fluid entry into the tissue (swelling).
The itchy part I’m still not quite so sure about. Histamine causes your blood vessels to dilate, and is therefore released in the process I described above. But apparently it also irritates nerve endings, and produces that itch. Believe it or not, I am actually regretting my decision to leave every single textbook in NJ this summer. I’m not totally convinced by this explanation, I’ll get back to you if I get to the bottom of it.