In the backwoods, you share with friends. But if hands go unwashed, you could be sharing nasty things that your cohorts would rather avoid.
"It's a good guess that the simple act of hand washing has prevented more illness and saved more lives than any other single measure in the last century," reports the University of California, Berkeley Wellness Letter (March 2001). And this "simple act" cannot be forgotten on backcountry trips if you want everyone to stay healthy. All you need is biodegradable soap and water. You can do a worthy job in as little as 15 seconds, even with cold water. Wash the fronts and backs of your hands, between your fingers, and under your fingernails (which you should keep short). Rinse and dry completely. If you have it, slather on hand sanitizer—which helps kill germs but is no replacement for washing—as a little extra health insurance. Now you're a safe sharer.
Remember to wash at least 200 feet from a water source. Untreated water works fine for hand washing because the soap, scrubbing, rinsing, and drying process removes cooties, even those in the water. If your hands were clean prior to dipping them into a stream, then the dip will not add significant germs to your hands, especially if you wipe them dry.