This week's question comes from Morning Brief reader MaryBeth, who asks, “I used to think humidity was the reason I felt miserable in the summer, now I understand it’s dew point. How did we avoid the dew point for so long when it seems to be the culprit? Every time I’ve googled this, the explanation is very confusing. Can you give an explanation that a 5th grader would understand about the difference between dew point and humidity?”

Meteorologist Sara Tonks: Webster’s Dictionary defines “humid” as “containing or characterized by perceptible moisture, especially to the point of being oppressive”. And that is part of the problem.

First, let’s start with what dew point is.

Dew point is a measure of how much water vapor (the gas state of water) is in the air.

Picture a jar halfway full of marbles. Dew point tells you precisely how many marbles are in the jar.

A higher dew point directly means that there is more water vapor in the air. So when you’re describing the air as being “muggy” or “humid”, what you’re feeling is the large amount of water molecules in the air.

This is also what makes your hair frizzy, because your hair is encountering and absorbing more water.

Then there’s relative humidity, which is a measure of how much water vapor is in the air relative to how much water vapor could be in the air.

Going back to our jar analogy… relative humidity tells you how full of marbles the jar is. But it doesn’t tell you how big the jar is, so you don’t know the actual number of marbles in the jar.

So a relative humidity of 50% means the air is holding half as much moisture as it’s capable of holding.

Now let’s beat the jar analogy into the dirt. If you’re producing marbles (sweating), but the jar is full (relative humidity is at 100%), you can’t put your marbles into the jar, so you’re left holding them.

And just like that, you’re left sweaty and gross.

So they do each have their merits, but the dew point is what actually tells you how wet the air is and therefore how muggy it feels.

Sara Tonks is a content meteorologist with weather.com and has a bachelor’s and a master’s degree from Georgia Tech in Earth and Atmospheric Sciences along with a master’s degree from Unity Environmental University in Marine Science.