Jen Theisen was at the 10-mile mark of a 16-mile July hike at Afton State Park southeast of St. Paul when it happened.

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"My lower legs felt a little prickly," the 46-year-old Crystal, Minn., woman recalled. "And then I knew it was starting."

She knew, also, what would come next: a reddish rash spreading across her lower legs, turning bright red by the following day. An uncomfortable, if not exactly painful, itching would last for a couple of days.

It's a familiar and unwelcome experience for Theisen. It's also known to Kaitlyn Bhoopal, a nurse practitioner at Twin Ports Dermatology, although Bhoopal has not experienced it herself.

"It shows up as red on the skin and can be a little bit purplish in appearance," Bhoopal said. "It can be kind of bumpy or look like hives, and the sensation is that it's very itchy and it can be painful and burning."

Bhoopal knows it as exercise-induced vasculitis. Theisen knows that term as well, but describes it as hiker's rash. It's also variously described as golfer's rash, Grand Canyon rash or Disney rash.

Why it happens

Whether it's associated with waiting in line for roller coasters, walking the back nine or traversing the Superior Hiking Trail, it's all the same thing, and has the same cause.

"It tends to be when someone is exercising during warm weather, especially humid weather," Bhoopal said. "The blood that's down in your lower extremities isn't able to make it back up to the heart. So then that leads to blood pooling in those smaller vessels, and that's what causes the inflammation and irritation."

Theisen discussed the rash topic with a reporter recently at Beaner's Central coffee house. She was accompanied by her sister Claire Lawrence, 43, of New Richmond, Wis., ahead of a quick backpack hike (two nights of camping) from Lake Agnes to Cascade River State Park on the Superior Hiking Trail.

It's easy to see that the two women are a match as companions as well as sisters, with quick wits and ready laughs. That's a good thing, as they are preparing to hike the entire 310-mile length of the trail in September.

The two hope conditions will be cooler by then, because for Theisen, the rash tends to occur when she hikes at least 10 miles at a temperature of 80 degrees or higher, she said.

Not poison ivy

Drawn into hiking when she agreed to lead her son's Boy Scout troop six years ago, Theisen didn't wait long before her first experience with hiker's rash.

"It was on my very first backpacking trip in Glacier National Park in 2012," she said. "Everybody told me I had poison ivy. I didn't."

Theisen would come to know what she was dealing with, and there would be 10 or so other incidents, she said. The most unsightly rash occurred after a Boy Scout hike around Medicine Lake in Plymouth, Minn., on a sultry day a couple of years ago. But what really got under her skin was that Afton State Park hike in July.

"To be perfectly honest, it ruined all the fun of my 16-mile hike," she said.

Theisen took to the internet, venting her frustration on her blog,, and asking for input via the Facebook pages belonging to the Superior Hiking Trail and to All Women All Trails.

She received more than 200 responses, ranging from "aloe" to "Is that what that is?" to "epsom salt baths" to "elevate legs" to "I don't think elevating your legs is going to help."

Theisen also went to see her doctor, just to make sure. Happily, she tested negative for any abnormalities.

For someone who merely experiences the rash and itching, that's likely to be the case, Bhoopal said.

If it's a more serious form of vasculitis, "it wouldn't just be associated with exercise, and the patient would experience headache, fever, weight loss, generally not feeling well," Bhoopal said.

If those symptoms accompany a rash, you should seek medical help, she said.

What works (sort of)

The best way to prevent garden-variety exercise-induced vasculitis is to wear compression socks and garments, Bhoopal said. "That just helps to provide support to the vessels and encourage the blood to return back to the heart."

Theisen has been wearing compression socks on hikes for four years, she said, and although they haven't always prevented hiker's rash, she does think they diminish it. She has received other advice, some of which seems a little out there.

"I'd say one of the weirdest things I heard was to drink ionized water," Theisen said. "And then the person told me that they were an ionized water filter sales person."

But she gives more credence to other suggestions. Among them:

• Cool off your legs in water.

• Elevate your legs.

• Use an aloe vera gel to cool your legs, along with a lavender spray or lavender oil.

• Use an antihistamine. Xyzal has come to be her antihistamine of choice, Theisen said.

Theisen put much of that into practice on that Agnes Lake-Cascade River hike, she reported later. She started to feel a telltale tingling in her legs when they took a break, Theisen said, but it was at water. She soaked her legs in the cold water for about 20 minutes, then elevated her legs and put some aloe on them. That "prevented it from 'fully blooming' into a full-on rash," Theisen wrote in an email.

Theisen has rejected one piece of advice.

"My second dermatologist said the only cure for it is to stop hiking," she related. "And I was like: Phhhht."

Theisen's advice for the rest of us runs in a different direction. Yes, you probably should get checked out if there are other symptoms, she said, but otherwise: "Get out anyway. Don't let it stop you. And don't let people convince you that it's something serious."

A few moments later, she added one more bit of advice, possibly with tongue in cheek:

"Don't be afraid to talk about your embarrassing problems on the internet."