Meteorologist Dave Epstein is our go-to person for pressing weather questions on everything from winter blizzards to summer droughts. He’s also a horticulturist, meaning he’s an expert in anything that grows leaves and flowers. GBH's Morning Edition asked our audience for weather and gardening questions, and Epstein graciously answered them on the air. This transcript has been edited for clarity.
Why do we get dry skin in the winter?
There’s a meteorological reason behind heavy hand cream season, Epstein said. And to understand which days will be drier, it helps to have a sense of dew points and relative humidity.
In the winter, Boston gets colder air from Canada and even the Arctic traveling down to the area. And as the colder air comes in, dew points get lower.
The dew point is a measure of the atmospheric temperature. Below it, water condenses and dew can form. Generally speaking, the higher the dew point, the more humidity can be in the air.
Another common measure is relative humidity: A measure of how full the air is of the moisture it could have.
Relative humidity by itself can be misleading, Epstein said. On cold days, a high relative humidity doesn’t translate to much moisture in the air.
“If the dew point is down at 10, what that tells us is the air can't hold much moisture,” Epstein said. “So even if you have a 90% relative humidity at a 10 degree dew point, there's so little moisture still that it doesn't matter.”
Picture a day with a high dew point and low relative humidity as a half-full pool, and a day with a low dew point and high relative humidity as a full glass of water, he said.
“A pool can be half full and have way more water than an 8-ounce glass that's completely full,” Epstein said.
All of that to say: On less humid days, dry skin abounds.
“When you get those dew points down in the single digits and even below zero — we had dew points last winter, a couple of times in the -5 to -10 degree range — there's not much moisture in the air,” Epstein said. “And so what moisture you have in your skin gets evaporated really fast. And that's why your hands and your lips and everything else dry out so much.”
So what can the dry skin-averse do? Keep moisturizers and lip balms handy, Epstein said. Keep showers shorter and not too hot, as the heat can also contribute to dry skin.
Humidifiers can help too, he said. And when the air is dry, wood furniture can also suffer, he said.
“Your wood furniture could use some furniture polish that has some cream in it in the winter because if your house is really dry, the wood can crack,” he said.