So I've seen that most people who hike in deserts wear something over their mouths, a bandana, a buff, whatever. I've also had a few comments on "preserving hydration" that way, as in it prevents you from expelling water vapor at as high a rate.

I was wondering if there's any truth to that. I figure that if there is, we'd all do it to shave weight (water on our backs).

Anyone care to weigh in?

I wonder how much of this has to do with simply covering more of the skin, reducing exposure to sun and wind, thus, slowing water loss through slower evaporation; the arms, legs, torso and head are covered, why not the face, too, I suppose?

I don't have a clue if its efficacy actually justifies carrying less water.

I'm not believing you can actually force sweat back into your pores, or prevent it from coming out. Or that it would be a good thing. You sweat for a reason.

yeah, very good points. Probably just bogus "in my experience" things mixed with less skin exposure.

I think their argument was that the air you inhale would have more moisture.

I vote for not true.

""I think their argument was that the air you inhale would have more moisture.""

Of course, simply wrapping your face with a piece of cloth won't inherently add moisture to the air one is breathing. If the piece was saturated with water, it could feel cooler, perhaps, leading to the impression of staying more hydrated; I suppose that if the wet bandanna actually cooled you off a bit, you might sweat less and save a bit of water. Ironically, if that were true, it might take water to save water? But that also makes me think of those humid conditions in the South - if the bandanna was so wet that it prevented evaporation, would it still feel cooler? But then again, if it were that hot and dry outside, the bandanna wouldn't stay wet very long anyway without constant soaking, adding to the irony!

The best way to prevent losing moisture via the mouth is to close it and breath through the nose. Less mucosal surface area exposed.

WHile nothing can force sweat back in to your body, lowering your direct sun exposure while allowing for air movement can cut down on your water loss, as well as protecting your skin. Just because you are covered does not mean you will sweat more. I spent a summer in Iraq with temperatures in the 140's and we always wore loose fitting long sleeves, as did the Iraqis.

Once your skin burns, even a little, it diminished its ability to effectively thermoregulate.

One of the ways you lose water is through breathing - your mucous membranes moisturize the air as you breath in, to aid in the lungs absorbing O2. This moisture then leaves your body when you exhale, dehydrating you. By putting a bandanna or some other cloth that will absorb moisture over your mouth and nose, you can potentially save some of that moisture, as the inhaled air will have to go through the cloth before it gets to your mouth/nose. The cloth, damp from your exhaled breath, releases some of its moisture into the dry inhaled air, thus saving a few milligrams of water. Over a day, it might save you a measurable bit of water.

That's the theory, at any rate. I don't know if it's ever been tested. It would only work where the air is quite dry - in humid air, it would serve no purpose.

Anecdotally, pictures often seem to show people who live in desert environments covering their faces, except for their noses and eyes. I wonder if there has ever been any scientific experiments done to prove/disprove this use.

It's not completely bs but in hot climate the effect is not probably big enough...

This is actually something mountain climbers do when climbing really high. Besides bandanas, there are even more effective masks that are specially designed for this.

But the idea is not to force water back in! Surface of the lungs is designed to be moist. Dry air evaporates more moisture from lungs than moist air - if you can moisture incoming air, the lungs do not dry as much thus the body does not need to release more liquid to the surface of the lungs --> helps to prevent dehydration.

Google probably knows more about this with keywords like mask khumbu cough

I do not know if there are benefits in hot climate, but at least those specific masks are way too hot to use if the temperature is more than -15C/5F. I'm sceptic about the idea in hot climate, as the mask preserves heat in incoming air too --> excess heat needs to come out as with sweat. The difference of the moisture capacity in air is also much bigger if the air is really cold, and that makes the system more effective if the outside air is much colder than body heat.

Edited by anttipeltola on 07/23/2011 08:19:44 MDT.

Anecdotally, it's not BS by any means. It definitely works in DESERT (ie DRY) climates. High humidity will decrease the efficacy, probably to the point of being useless or detrimental. For the record I grew up in the deserts of AZ and also spent many summers in the humidity of So. Ill, so I am particularly aware of my own hydration levels. Also the Buff I used was the original buff which is made of polyester.

I'm a recent convert to using a buff to cover the face during summer hiking. I experimented with it just this past spring break in Death Valley. I hiked out in the cool morning (started in low-mid 70s) to some dunes using my normal technique of uncovered face. Naturally I was constantly sipping on my camelbak to moisten my parched throat. On my return hike (starting around noon, temps rising to high 80s low 90s) I was fed up with the dust and sun reflection so I wore my buff balaclava style. I instantly noticed a dramatic improvement in comfort! Not only did it keep grit out (which soaks up moisture) but it created a micro-climate for my nose/mouth.

It's this micro-climate that makes a HUGE difference in comfort. I drank considerably less water on the way back in without feeling dehydrated at all. Even with the higher temps and lower humidity they brought. Obviously this wasn't scientific so I didn't measure my body's water content or anything but I can tell you I FELT better which may be just as important.

I will go so far as to hypothesize that some kind of light weight face covering does decrease moisture loss (ie dehydration). The reasoning is actually the same concepts as the psolar masks and similar used by Alpinists and cold weather adventurers.

The buff traps humidity creating a micro-climate that is considerably more humid than the ambient air. This in effect provides a "pre-moisturizing" chamber similar to the function of the sinuses (which is why nose breathing in heat is recommended). This is conserving/utilizing your exhaled moisture to moisten the inhale.

On top of this the Buff absorbs some moisture and holds it. As you inhale you force hot and dry air through the fibers. Heat is removed from the air to vaporize the moisture collected in the fabric fibers (as well as warm the fibers directly) which cools the inhale breath. It's definitely noticeable, especially when you take a big/deep breath in. With cooler incoming air, less moisture is lost as well.

Again this "science" is purely hypothetical but I would bet money that a proper experiment would show some benefit to wearing a light face covering.

CONS: There are some. The micro-climate can become very humid, and with the perceived reduction in air flow it can feel stifling to wear the face mask. This is really more of a psychological issue that passes once you get used to it.


The polyester buff fits somewhat snug around the face but has a loose weave so does not trap much heat. I wonder if a cotton bandana or loose weave nylon cloth (both of which are far more hydrophilic than polyester) may provide more benefit by absorbing more moisture. Wool may do the same but would have to be fit loose enough to allow air to flow between your skin and the fabric, it's just too insulating when fit snug (I can wear snug wool shirts to about 75F before I'm looking for a loose and stinky synthetic).

I do now always wear some face covering in dry (and especially hot) environments. Here I am representing the American Bedouins:

I did my Peace Corps service in the Sahel, where the local herders all wore a good 4m plus of fabric wrapped around their head/face. I ended up buying 2m of the same fabric myself, enough to wrap around my head and face while staying on snug. Combined with a long sleeve Capilene 1 shirt, and my baggies, I was a happy camper in temperatures over 100F. I definitely noticed the micro-climate action happening around my nose and mouth. I also feel like the fabric acts as a heat sink as it cools from evaporation.

Given that this sort of head-ware is common throughout the Sahara and Sahel, especially amongst nomadic peoples who are constantly on the move in scorching temperatures, I would make a case for it being a legitimately beneficial technique. Experiment for yourself and see if more coverage, especially head and face, makes a difference. I was definitely happy I did.

From an UL perspective a buff might make more sense than carrying 2m of fabric. Next time I'm near a desert I'll try it out myself.