Why do fingers wrinkle in water?

Why do fingers wrinkle in water?

　You may find that your hands and feet will wrinkle¹ when you are washing clothes, taking shower and swimming. Do you know why?

　Even though you cannot see it, the outermost layer of your skin is covered with a special oil known as sebum². Sebum makes your skin waterproof. When you stay in water for a long time (at least 10-15 minutes), the layer of sebum gets washed away.

　The tough outer layer of your skin is made up of dead keratin cells. Once the layer of sebum is removed³, these dead keratin cells in the skin of your hands and feet start absorbing water. This causes the skin to expand.

　But it can’t expand evenly⁴. It goes outward in some places, it goes inward in other places. That makes wrinkles.

　Don’t worry, your skin will be smooth again as it dries.

Notes:

1. wrinkle v. 起皱 2. sebum n. 皮脂

3. remove v. 除去 4. evenly adv. 均匀地