Continuing “Joe’s Answer Bag Week”:
I don’t know if this question would be up your alley but I was wondering why your skin burns when you run hot water over a scratch,blister, or cut.
First off, excellent Tumblr name. Velociraptors are the most clever of dinosaurs, and I like to think they’d have an appreciation for crispy pork products.
I like to think any science-related question is up my alley. It’s a very welcoming, curious alley.
I think we’ve all been in this situation, right? Fall down, go boom, scrape skin, wash scrape, OW OW OWWWWWW. Insert common (but misused) antiseptic methods like alcohol and hydrogen peroxide, and you get the same effect. Why does a scratch, blister or cut (or burn, for that matter) hurt more when water hits it?
It starts with inflammation. Inflammation is a very generic term for how your body’s vascular system (blood and fluid transfer) reacts to injury or infection. When you look at your skin, you see what appears to be one uniform type of cell (called a fibroblast). But if you were shrunk to the size of Dennis Quaid in Innerspace, you’d see that there were actually many types of cells that make up your outer and inner dermis.
Some of these cells are on constant alert for intruders or danger, the sentries of your outer boundary. If they sense tissue damage, infection, or a burn, they sound an alarm and call for help. Instead of fighting off the infection directly (like say, a bacteria-covered splinter), they secrete chemicals called inflammatory mediators or cytokines. This has a whole cascade of effects.
Blood vessels dilate (causing redness), forming leaks in your capillary walls. These leaks allow fluid to escape into your tissue, causing the swelling and warmth you associate with blisters or scrapes. These leaks also allow white blood cells to migrate out of your blood and into your tissue to fight any infectious agents. The white blood cells actually follow the chemical signal from the inflammation right to the injury, like hounds on the trail of a fox.Your increased sensitivity to pain (called hyperalgesia) is caused by other signaling molecules that are released by the injury, like bradykinin (brady-kyn-in). Bradykinin chemically changes the way that your pain neurons fire, making it easier for them to signal pain, and making things hurt (like water) that normally wouldn’t. This is probably an adaptation to keep you from making an injury worse.
Bonus fact: Compounds in aloe vera actually inhibit the bradykinin molecule from working, which is why it feels so good to rub it on burns.
On to the next one …