This Week's Experiment - #301 Scratch Science
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.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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