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Why does your skin get so dry in cold weather patterns?

FILE -- Bus riders, bundled against the cold, wait for the next ride as a snow storm moves in on the area in Portland, Ore., Wednesday, Dec. 14, 2016. (AP Photo/Don Ryan)

Seems strange living in one of the mildest, humid places around that you'd ever have to deal with dry skin, but as soon as the thermometer drops into the 20s and the north wind blows, Chapstick and skin lotion become must haves to get through the week.

Why is that? There's a few reasons.

First of all, cold air doesn't hold as much moisture as warm air to begin with. So just being outside on a cold, sunny day in itself will have less moisture in the air than being outside on a sunny day in the 50s, everything else being equal.

But our really cold days come with a similar feature as our really hot days -- a dry, offshore wind. It's the only way to hold back the moist Pacific Ocean air. In the winter, the cold air comes from via the interior of British Columbia through the Fraser River Valley and/or a cold Eastern Washington. Temperatures in the interior of B.C. are very cold -- sometimes in single digits or even below zero (Fahrenheit) with even lower dew points -- the temperature needed for air to become saturated.

When that cold air blows into Western Washington, so too does the dry part. On Sunday, Seattle was sitting at 33 degrees with a 31 degree dew point -- that's not terribly dry. But once the Fraser wind began spilling into Western Washington, the humidity crashed. Bellingham on Monday had a temperature of 28 and a dew point of just 5 degrees. Seattle was only down to 30 degrees, but its dew point was down now to 15 -- a 53 percent relative humidity, but as I mentioned earlier, this cold air can't hold as much moisture so it's a drier 53 percent humidity than what you feel on spring or summer days. The dry air makes it easier for moisture to evaporate from your skin.

But our attempts to thwart the cold make it even *worse*. When you go home and turn on your furnace or car's heater, it's adding heat -- but not moisture -- to the air. So while it's 30 degrees with a 15 dew point outside your home, it might be 68 degrees with a 15 dew point inside your home -- a relative humidity at a skin-cracking 13 percent.

Can't you just use a humidifier?

Yes, but there's a trade-off. In dry situations, a humidifier works akin to a swamp cooler. In the desert on triple-digit heat days, the humidifier cools the air because the process of adding moisture to the dry air causes it to evaporate, which saps energy from the air and cools the ambient temperature.

But in the winter, your furnace is doing the opposite effect. So running a humidifier will cool the air and battle against your furnace. Eventually, you'll manage to make the air more humid but it'll come at the expense of the efficiency of your heating system, requiring more energy to maintain a comfortable temperature inside your home. But if you find your home is just too unbearably dry, it might be an option.

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