Science | Science Experiment of the Week 10 | 301 - Scratch Science

Histamines, Antihistamines, Mast Cells - We have all gotten a scratch now and then, but most people never learn the science involved. If you think about the science, you might not notice that it hurts so much.

This Week's Experiment - #301 Scratch Science

These experiments are from Robert Krampf - The Happy Scientist

The week's experiment is a result of a question that Lisa asked about scratches. We have all gotten a scratch now and then, but most people never learn the science involved. If you think about the science, you might not notice that it hurts so much. We won't hurt ourselves today, so if you are itching to know more about how your body works, you will need:

your skin

Have you ever had a mosquito bite? Or been scratched by a thorn, a cat, or maybe a 70 pound Labrador? What happened to your skin? We can investigate that under more pleasant conditions. Pick an area of skin that is fairly tender. I picked the skin on my right side, just at the ribs. Now pretend that you have a mosquito bite there. If it helps, tell yourself that you are not allowed to scratch and it will start to itch fairly quickly. Now scratch the itch. Don't hurt yourself and don't break the skin. Just scratch the itch. Then watch the skin carefully. If you are light skinned, you will quickly see the scratches turn red. If your skin is darker, then you may not see that. Either way, if you look carefully, you may see that the skin has swollen and risen up slightly along each scratch. The area will feel warm or even hot. It will be very sensitive to touch.

Why does this happen? Your body contains special cells called mast cells. When they are irritated, such as being scratched, they release all sorts of chemicals. One of these is called histamine. Histamine causes tiny blood vessels to release blood into surrounding tissues. This causes the area to look red, feel hot and become swollen. The blood cells can help fight infection in the tissue, but the swelling can put pressure on nerves, causing more itching or pain. Scratching a mosquito bite releases histamine. Besides causing swelling, histamines sensitize nerves, making sensations such as pain or itching more intense. Scratching actually makes the itching worse. The more you scratch it, the more histamine you release and the more it itches. A trick that I learned is to use your fingernail to press into the center of the bite several times, making a star shaped pattern. This helps disperse the mosquito spit (Yes, the initial itch is caused by mosquito spit.) without releasing too much histamine.

The histamine reaction can also be triggered by things you are allergic to. It may just be a yummy strawberry or peanut butter, but if you are allergic, your body mistakenly identifies it as something dangerous. This triggers the histamines, and you get a rash or worse. A histamine reaction in the airway can cause the tissue in your nose, throat and lungs to swell. That makes it difficult to breath. When that happens, we take something to stop the histamines, an antihistamine. Many medicines for colds and flu contain antihistamines. Some people are so allergic that they have to go to the hospital to control the reaction.

After reading all this, the histamine reaction from your scratching has probably ended and your skin is back to normal. As long as you don't think about that imaginary itch, you won't have to scratch any more. In the mean time, I am not allergic to turkey, so I will have a snack before bedtime. Have a great week.

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