Why does a wet hand feel cold?
Brrr! When you climb out of a warm bath, your wet skin can feel chilly. Here are two cozy, warm hands. One hand we keep wet… and one hand we let dry off. In a moment, one of them turns cold. Ready to guess… which one — the wet hand, or the dry hand?
After you watchWhy does a wet hand feel cold?
The short answer
A wet hand feels cold because the wetness dries away, and as it flies into the air it carries a little of your skin's warmth with it. The hand that dries off turns cold, while a hand that stays wet keeps more of its cozy warmth.
Try this next
- What if you blow on the wet hand? Blow gently on a wet hand and then on a dry one. Guess first: which feels colder, before you try it?
- What if you wrap the wet hand in a towel? Guess whether a covered wet hand still turns cold, then dry one hand in the open air and keep the other tucked away.
The whole story
How it works
Tiny bits of water are always leaping off a wet surface into the air — that is what drying is. Each bit that flies away takes a little heat with it, so the skin left behind cools down. The faster the water flies off, the colder the skin feels. A hand that stays wet has not given its warmth to the air yet, so it stays warmer.
What people get wrong
Many little kids think the cold lives inside the water itself — that the drop is icy. But the drop and your warm skin start out the same coziness. The chill is not hiding in the water; it is made as the water dries off and flies away, carrying warmth with it.
The catch
Drying fast cools you quickly, which feels great on a hot day — but the cozy warmth is gone. Staying wet keeps you warmer for now, but you stay wet and drippy for a long time.
Questions kids ask
Does the water have to fly away for the hand to feel cold?
Yes. The cold comes from drying. As the wet bits leap into the air they carry warmth away, so a hand that stays wet does not chill nearly as much as one that dries off.
Why does blowing on a wet hand make it feel colder?
Blowing sweeps the wet bits off faster, so more of them fly away and carry away more warmth. The faster the drying, the colder your skin feels.
Is the water itself cold?
No. The drop and your warm skin start the same coziness. The chill is made while the water dries, not hidden inside the drop.
Talk about it
- We have two warm hands — guess which one turns cold, the wet one or the dry one?
- Where do you think the wet goes when a puddle dries up?
- Why do you think you shiver when you step out of the bath?
For grown-ups
This is evaporative cooling, told at a four-year-old's altitude. To turn from liquid into vapor, each water molecule must absorb energy (its latent heat of vaporization), and it draws that energy from the skin and water left behind, lowering their temperature. It is the same physics behind sweating, hand sanitizer's icy rush, and stepping out of a pool into a breeze. Alcohol simply evaporates much faster than water, so it cools even more.
Keep going
What else makes you wonder?
- What if you blow on your wet hand — does it feel even colder?
- Why do you shiver getting out of the bath but not while you are still in it?
- What other wet things get cold when they dry?