I once lost all the feeling in my toes for three months from “trenchfoot.” I was lucky, in the end, that I suffered no permanent damage.

How did this happen? Well, you might guess that I froze my toes off in pursuit of an extreme adventure—high-altitude mountaineering or dogsledding across the North Pole—but no. I was backpacking, in June, near my home in Wyoming.

I started my five-day hike at a popular entry into the Wind River Range in sunny, warm, even hot conditions. In a matter of hours I gained enough elevation that I encountered winter snow that hadn’t yet melted off, so I ended up hiking through freezing puddles of water on the trail. My boots became saturated with cold, icy water, and I hiked on. On the second day it started to snow on me, and it grew much harder to take the time and effort to stay warm and dry.

At some point my feet got cold. Of course, I know when they got cold—it was when the icy water poured in over my boot tops. What I mean is, at some point they stayed cold and I didn’t do anything about it. And so my feet stayed cold for hours and hours, setting the stage for trenchfoot, more accurately known as “immersion foot” or a “nonfreezing cold injury.”

As I have since learned through the Wilderness Medicine Institute, the physiology is simple. In response to the moisture and temperature, my body acted to narrow the tiny blood vessels that fed my toes. This is a standard reaction to cold exposure called “vasoconstriction.” Smaller tubes meant less blood got through, so the other tissues in my feet, the skin, bones, nerves, muscles, did not get the oxygen that they needed to stay healthy. Nor did they get cleaned of the normal cellular waste they generated, which is supposed to be flushed away by the blood, filtered by the kidneys and eliminated in my urine. This waste built up.

The first tissue to be affected drastically was nerve tissue, which seemed to stop functioning. I perceived this as numbness that went away that evening when I warmed my feet, then came back the next day and persisted after the second cold day no matter how much I warmed my feet. In fact, the sensation of numbness in my toes persisted for about three months after I finished the trip.

My skin became red, itchy and painful when I warmed it, but that was about it. My feet returned to normal after three months, and I didn’t experience immersion foot at its worst: ulcers, infection of those ulcers, permanent nerve dysfunction, tissue death, amputation. All of these are possible.

You’d be better off not repeating my mistakes. The main rule is to never tolerate cold, wet feet. This starts with planning your activity and choosing appropriate footwear. Boots and shoes should fit well (and not squeeze the feet), insulate for the cold, and keep socks dry. Because any boot can become saturated if conditions are wet enough, consider using vapor barrier socks for your dampest slogs. Or, you can improvise these by using plastic bags to line your boots.

If your feet do get wet, take the time to dry them off, massage them warm again and change or at least wring out your wet socks. If you’re camping, sleep in a pair of dry socks that you keep at the bottom of your sleeping bag to guarantee that your feet get to stay warm and dry overnight at least.

Simple precautions and a little discipline will help you enjoy the wet conditions and not suffer from the cold.

John Hovey is an REI guest blogger and an instructor at the Wilderness Medicine Institute, a division of the National Outdoor Leadership School (NOLS).

Wind River Range and trenchfoot photos courtesy of John Hovey.