Humidity

Humidity is the amount of water vapor in the air. Water vapor is water in its gas form, and you cannot see it. When humidity is high, the air feels sticky and damp. When it is low, the air feels dry. Humidity plays a big role in weather and how comfortable we feel.

Measuring Humidity

Scientists measure humidity using a tool called a hygrometer. Relative humidity tells you how full of moisture the air is compared to how much it could hold. At 100 percent humidity, the air is holding all the water vapor it can. At 50 percent, the air is holding half of what it could hold.

Why Humidity Matters

High humidity makes hot days feel even hotter because sweat does not evaporate easily from your skin. Low humidity can make your skin and lips feel dry and cracked. Humidity also affects weather. When humid air rises and cools, the water vapor turns into clouds and rain.

Fun Facts

• Tropical rainforests often have humidity levels above 80 percent.
• The Atacama Desert in Chile is so dry that humidity can drop close to zero percent.
• Hair can actually be used to measure humidity because it stretches when the air is moist.

Did You Know?

Some old-fashioned weather stations use human hair to measure humidity. The hair stretches when the air is humid and shrinks when it is dry. A single strand of hair can measure humidity surprisingly well!