Do your fingers and toes easily get cold? You may be experiencing Raynaud's Phenomenon. As an instructor at the Wilderness Medicine Institute of NOLS, I share my friend Abby's story and tips on how you can avoid it happening to you.

Abby and I were dayhiking in the Columbia River Gorge of Oregon, headed up to see Multnomah Falls. The walking was easy, the day was clear and beautiful, and we were having a grand time immersing ourselves in the lush greenery of the Pacific Northwest.

We stopped at the falls, took a seat, and broke out our lunch. Thirty minutes later, full and happy, I suggested we pack up to go. "Aw, man," Abby said. "Look at that." She ripped off her gloves with her teeth, and held out her hands.

Just sitting still for half an hour in 55-degree weather had rendered her fingers blanched white, numb, and clumsy enough that I had to help her re-glove and zip up her daypack.

I was stunned. Here I was comfortable in a light jacket which was only half zipped while Abby, wrapped in down, could no longer move her fingers.

She suffers a condition known as Raynaud's Phenomenon.

Human beings regulate temperature largely via bloodflow shunting. When we get too hot, for example, our vasculature adjusts by widening the blood vessels closest to the skin. This allows more blood to circulate there, which in turn causes the skin to feel hot and appear red in color as it conducts excess heat out of our bodies.

In cold weather, the opposite can occur: Our bodies maximize the odds of survival by hoarding bloodflow for the most important organs, like the brain, heart, and lungs, and sacrificing bloodflow to the extremities by constricting blood vessels like the small arteries that service your fingers and toes.

There's an emotional, sympathetic nervous system component to vascular shunting, too. Just like you can blush when you become embarrassed (even if you aren't actually too hot), some people experience exaggerated vasoconstriction of their hands and feet far earlier than would be considered normal and appropriate.

The technical term for this condition is "Raynaud's Phenomenon", named for Dr. Maurice Raynaud of France who researched it in the mid-1800s. More recent research estimates that about 8% of women and 5% of men suffer from the condition, which presents mainly as skin color changes and pain in the digits.

Raynaud's Phenomenon has 3 phases. First, blood vessel dilation starves the fingers and toes of blood, leaving them pale, white or yellow. The whitened coloration may affect only some of the digits and often has a sharp demarcation across the finger, beyond which the skin appears normal. The second color change is to blue, which occurs because the tissues are no longer receiving enough oxygen. Finally, when the attack subsides, the skin becomes red and painful. It may swell and feel itchy or like pins-and-needles.

This problem is usually an inconvenience for the sufferer, but in the outdoors it becomes downright dangerous. Raynaud's Phenomenon patients must be constantly on guard for they are more susceptible to chilblains, trenchfoot and frostbite and will develop these conditions more quickly at lower altitudes and at warmer temperatures than others with normal cold response.

Here are 8 guidelines for preventing and treating a Raynaud's attack. (Note that they are pretty useful for keeping your fingers and toes warm too, even if you don't have Raynaud's!)

1. Keep your core body warm.
To some degree (pun intended) your body decides to shunt blood based on how cold your core feels. So layer up for the cold, even in mild temperatures. Read the REI Expert Article article on layering for more information on how to dress.

2. Insulate your hands and feet especially well.
Choose a pair of warm winter mittens (preferred) or gloves and wear them religiously. Same for boots. You may be able to prevent an attack by keeping your fingers warm. Visit REI's product finder for gloves and insulated boots to see many options.

3. Avoid emotional stress.
If you get scared, you activate the fight-or-flight response in your brain. That's your sympathetic nervous system ramping up, which sends all your blood to your core. You need to stay both warm and calm to prevent an attack.

4. Avoid stimulants and vasoconstrictors.
These will chemically activate your sympathetic nervous system and also spur on a Raynaud's attack. Caffeine is out! Sudafed, Benadryl, and other decongestants and antihistamines are out! Nicotine? Do you really need me to tell you not to smoke? Well, add Raynaud's to your list of reasons tobacco is bad for you.

5. Get off the pill.
Hmmm, that sounds a little pushy. But studies suggest that estrogen-based contraceptives can aggravate Raynaud's. It might be worth visiting your doctor to investigate a progesterone-only oral contraceptive or other alternatives.

6. Warm whitened digits ASAP.
As soon as you can, immerse pale fingers or toes into warm water, wiggle them actively, and massage them. Don't stop until the color returns to normal. If warm water isn't available, use skin-to-skin rewarming. Tuck your fingers either under your armpits or up against your neck. Have a friend loan you their abdomen, and warm your toes against their belly. (Note that this will probably alienate you from some social groups.) DANGER: Be extremely careful attempting to warm your hands or feet with a campfire, stove, or other radiant heat source. Because you're numb, you are much more likely to burn yourself. Not good!

7. Pump blood to your extremities.
Swing your arms in large circles quickly to increase circulation to your fingers. Grab a tree for balance (after you put your gloves on, of course) and kick your legs back and forth, one at a time, in a running motion. Feel the circulation return to your fingers and toes.

8. See your doctor.
Raynaud's isn't always just Raynaud's. If you experience an attack for the first time, or if your condition is getting worse, then it could have a serious underlying cause and you want to get that checked out. Additionally, your doctor may prescribe drugs to treat Raynaud's Phenomenon.

To learn more about wilderness medicine, visit WMI of NOLS.