Haut
9 cards from across every topic, each citing a source. Tap one to open it in the feed.
- Goosebumps are a program for fur you don't have.
Every hair has a tiny muscle attached, the arrector pili. In cold or fear it contracts and raises the hair. In furred …
- How a wound becomes a scar in four phases.
First, haemostasis stops the bleeding within minutes. Then the inflammatory phase clears debris and microbes. From day …
- How sweat cools you even though it's body temperature.
You have 2 to 4 million sweat glands. It is not the sweat that cools you but its evaporation: every gram of water that …
- Pruney bath fingers aren't water damage.
The old story was that skin soaks up water and puckers. But fingers with severed nerves don't wrinkle at all. Wrinkling …
- SPF 50 doesn't protect twice as well as SPF 25.
Sun protection factor states what fraction of UV-B gets through: SPF 15 lets through 1/15 (about 7 %), SPF 30 about 3 …
- Shaving does not make hair grow back thicker.
A razor only cuts the shaft above the skin, not the root. An uncut hair tapers to a fine tip; a shaved one ends bluntly …
- The number in your weather app that matters more than temperature.
The UV index runs from 0 to 11+. From 3 upward the WHO recommends protection: shade, clothing, sunscreen. From 8 it's …
- Your fingerprint was finished before you were born.
The first ridges form from about week 13 of pregnancy, and the final pattern is set around week 15. Genes fix the basic …
- Your outer skin is never more than a few weeks old.
The epidermis renews itself roughly every 4 to 7 weeks. New cells form in the deepest layer, migrate upward, harden …