This has been a maddening few weeks for runners. One day, I'm out in shorts, tank top, and summer visor. The next, I'm pulling on gloves and my highlighter yellow vest so I don't freeze and/or get hit by a fog-draped car.

The yo-yoing area temperatures are wreaking havoc on runners, in both how we run and how we breathe. If you have asthma, you know what I'm talking about.

"This is very hard on the lungs when you have asthma," said Stanley Lane, head of allergy and immunology at Virtua Memorial Hospital in Mount Holly. "The fluctuations in temperature can tighten up the lungs and bring on difficulty breathing."

Rain keeps both the ground damp and humidity levels high, conditions in which mold thrives. A long stretch of cold weather with frost would kill it, but when the area is still seeing the random days that are 65 degrees and sunny, this allergy and asthma trigger is just going to keep growing.

Combine that with the relative high air pollution in the Philadelphia area, Lane says, and asthmatics - whether they have it as a regular condition or exercise-induced - are going to have trouble with their breathing when running outdoors.

John Vasudevan, assistant professor of clinical physical medicine and rehabilitation at Penn Medicine, says that even if you don't have breathing problems, the up and down in temperatures can affect how you approach running and elements of your running environment, like terrain. It's easy to forget that when the temperature fluctuates, the condition of running surfaces fluctuates, too.

"When it's colder, the same surface you're used to running on has changed its stiffness," he said.

While on a fellowship at Stanford University Hospital, Vasudevan treated a professional runner who after training for months in California went home for the holidays and continued his routines in Minnesota. He wound up with a stress fracture in his leg because his body wasn't acclimated to running on stiff, cold asphalt.

Vasudevan also says runners can make mistakes based on assumptions about the weather, like carrying water for a long run on a 65-degree day, but going without on a 40-degree day.

"It's very easy to think that hydration would change if it's a little bit cooler, but it's more tied to the amount of activity you do," he said.

What can you do, other than move to Florida or Antarctica for more consistent temperatures?

For asthmatic runners, Lane recommends warming up indoors first, which he says will make it easier to breathe when you go outside. If you have an inhaler, use it 15 to 30 minutes before you run, and if you're still having problems, run on a treadmill until we finally turn the corner into colder, frost-making weather.

For everyone, be smart about layering and hydration, and don't assume your favorite running trail will be the same with 20-degree temperature differences.

Here's one more: If it's foggy or dark, remember to don that highlighter yellow vest, or a blinking light.

Racing Schedule

Saturday: The Day After 5K, Lewes, Del. Register by 11:59 p.m. Wednesday at active.com

Next Sunday: Browning Ross Winter Series, Glassboro 5K. Register day of race only. For more information, go to tuffgangrunning.com

If you have an upcoming race to include in the weekly calendar, e-mail jquinn@phillynews.com.

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Follow Jen A. Miller on Twitter @byJenAMiller.