We all know about Montezuma's revenge and everyone has had it at one time or another. But what are the principle causes that plague backpackers? We list them below.

• Giardia and Cryptosporidia infestation from drinking unfiltered water.
• Bacterial infestation from drinking water contaminated by animals or leaking sewer lines.
• Eating off of dirty pots and pans (usually another form of bacterial infestation).
• Eating pink snow (yet another form of bacterial infestation).

Pink and Yellow Snow - Hopefully, everyone knows by now not to eat the yellow snow, and if not, ask one of your friends about it. However, pink snow is another matter. You have probably seen it in the spring, just as the snow is beginning to melt - pink snow that is sometimes faint and hard to see, but other times is red and stands out in marked contrast to the white snow around it. Pink Snow is actually caused by soil bacteria that encyst when the ground freezes in winter, yet rise towards the surface of the snow and come to life in the spring when the temperature rises. They live off organic matter that diffusses its way up into the snow from the ground below. These bacteria can give you a terrible case of the runs. So leave the pink snow alone. It doesn't taste very good anyway.