How does panting help dogs cool down?

1. After a game of fetch in the sun, the dog is hot. It stops, opens its mouth and breathes very fast with its tongue hanging out. This is panting. Why does it do that?
2. When you are hot, you sweat all over, and the sweat cools you as it dries. A dog is covered in fur and has sweat glands only in its paw pads. That is not nearly enough.
3. The wet surfaces are inside! Air rushes in through the damp nose and out across the wet tongue, again and again, up to ten times faster than normal breathing.
4. Look closely at the tongue. The moving air turns the water on it into vapor. Water needs heat to do that, and it takes the heat from the warm tongue.
5. The tongue is full of tiny blood tubes. Warm blood flows in, gives up its heat, and flows back to the body cooler. Bit by bit, the whole dog cools down.
6. On a muggy day the air is already full of water, so the tongue dries slowly and panting works badly. That is when a dog most needs shade, fresh water and a rest.

Tap each part of the dog to see how it helps with cooling. The round window shows the tongue very close up.

• Wet nose. Air rushes in through the nose. Inside, it passes over damp, curly surfaces, and water dries from them, which cools the blood there.
• Tongue. The tongue is big, wet and full of blood. When the dog is hot, the tongue hangs out and even gets wider, so there is more wet surface for the air to dry.
• Windpipe and lungs. Panting breaths are quick and small. Most of the air only goes in and out of the nose, mouth and windpipe, where the cooling happens, not deep into the lungs.
• Wet surface. A thin layer of water covers the tongue. Moving air turns it into vapor, and that change uses up heat from the tongue.
• Blood vessels. Tiny blood tubes run just under the wet surface. Warm blood comes in, loses heat and goes back to the body cooler.
• Paw pads. Dogs do have sweat glands, but only in their paw pads. On a hot day a dog can leave damp paw prints, but this cools it only a tiny bit.
• Fur coat. Fur traps air. It keeps a dog warm in winter and also keeps some of the sun's heat off its skin in summer. But it stops sweat from working, so the dog must pant.
• Body thermostat. A part of the brain works like a thermostat. When it senses the blood is too warm, it switches panting on. When the dog is cool again, it switches panting off.

Tap the ball to play fetch and heat the dog up. Change how damp the air is, and watch the vapor leaving the tongue and the thermometer.

Experiment: On which kind of day does panting cool a dog faster?

1. Slide the air to dry. Tap the ball, then watch how fast the dog cools.
2. Slide the air to muggy. Tap the ball again.
3. Compare the vapor from the tongue and the time on the clock.

What we found: Panting works best in dry air. Dry air has plenty of room for more water vapor, so the tongue dries quickly and heat leaves fast. Muggy air is already full of water, so the tongue stays wet and the dog stays hot for much longer.

Turn on JavaScript to try it yourself.

It is a muggy day and the dog is too hot. Choose shade and moving air, start the clock, and give water when it is needed. Cool the dog before 45 minutes are up.

When you run around, your muscles make heat. Your body gets rid of it by sweating: water comes out of your skin, and as it dries it takes heat away. A dog cannot do that. Its fur gets in the way, and its only sweat glands are in its paw pads.

So a dog uses the wet places it does have: its tongue, its mouth and the inside of its nose. By breathing very fast, it blows lots of air across them. The air turns the water into vapor, and that needs heat. The heat comes out of the blood flowing through the tongue and nose, and the cooler blood then travels around the body.

How well this works depends on the air. Dry air soaks up water quickly, so a dog cools fast. A breeze helps too, because it carries the damp air away. But on a muggy day the air is already full of water. The tongue stays wet, very little dries off, and the dog stays hot.

Panting uses up a lot of water, so a panting dog needs to drink. On hot days dogs need shade, fresh water and rest, and walks are best in the cool of the morning or evening. A dog must never be left in a parked car, because the air inside gets hot very quickly. If a dog pants very hard and seems weak or wobbly, tell a grown-up right away.

Key words

Panting

Very fast, small breaths with the mouth open, used for cooling.

Evaporation

When liquid water turns into water vapor, a gas in the air.

Humidity

How much water vapor is in the air. Muggy air has a lot.

Latent heat

The energy a liquid takes in to become a gas without getting hotter.

Thermostat

A control that switches cooling or heating on and off to hold a steady temperature.

Check your thinking

1. Why do dogs pant when they are hot?

   Show the answer

   Water drying from the tongue and nose takes heat away. Turning water into vapor uses heat. The heat comes from the dog's warm blood.

2. Why can't a dog cool itself by sweating like you do?

   Show the answer

   It has fur, and sweat glands only in its paw pads. Fur covers the skin, and the paw pads are far too small to cool a whole dog.

3. On which day does panting work worst?

   Show the answer

   A hot, muggy, still day. Muggy air is already full of water, and still air does not carry the damp air away. Very little can dry off the tongue.

4. About how much heat leaves a dog when 3 grams of water evaporate from its tongue?

   Show the answer

   About 7,200 joules. Each gram absorbs about 2,400 joules, so 3 grams take 3 × 2,400 = 7,200 joules.

5. Why must a panting dog have water to drink?

   Show the answer

   Panting uses up water, and a dry tongue cannot cool. The cooling comes from water drying off. No water means no cooling.