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One of the joys of trail running is that body fluids can be discarded almost anywhere. Most of us have perfected our nostril and loogie ejections (ie, snot and spit) to the point it is a subconscious endeavor. But do we leave behind anything that we should be personally recycling to our own bodies? As disgusting as it sounds, would it be better for hydration and electrolyte balance to swallow rather than eject?

Every runner occasionally experiences times when thick saliva seems to build up in the throat or when the nostrils partially block with mucous. It takes little extra physical effort to propel that spittle to the trailside or, by occluding one nostril at a time with the index finger, expel nasal secretions to first one side then the other (as my son, Scott, calls it, the “snot cannon”). We feel better afterwards and air seems to flow more readily into our lungs. Mother Nature absorbs and repossesses our effluents so efficiently that most of us leave little trace in the wilderness. This is exactly as it should be. But I had always wondered if helping Mother Nature hydrate might be at the expense of our own hydration.

A quick tour of the nasal and oral system will help enlighten our internal capabilities. Mucous membranes line the nasal and oral cavities. The amount of mucous production can vary greatly among individuals and is highly influenced by allergies, air-born irritants, and infection. We know from our worst colds that maximum mucous production can be remarkably high. Thanks to pollen, dusts, and other allergies we also know that a thinner, clearer mucous can also be produced in impressive amounts. Mucus membranes work tirelessly, even as we sleep. Ordinarily everything is politely recycled by swallowing, except for the small portion that ends up in handkerchiefs, Kleenexes, or trailside. So here comes the question posed by this article: are we losing anything important when we return spit and snot to the earth instead of to our own stomachs?

Mucous and saliva are composed of protein, water, and electrolytes. Particularly important are the concentrations of potassium (about 30 meq/liter) and bicarbonate (50-70 meq/liters) which run approximately 6 and 3 times their respective concentrations in plasma. Sodium concentration is about l5 meq/liter. Bicarbonate loss increases the work of the kidney to reabsorb and re-form this compound, which is needed to buffer the lactic acidosis resulting from endurance exercise. The importance of maintaining general fluid and electrolyte balance is a well-documented essential for all cramp-free muscle performance, and it appears that there are high concentrations in the mucous and saliva we leave on the trailside. So we just have to figure out if the volume is significant.

The amount of saliva in each expectoration averages between 4cc. and 20cc (it wasn’t much fun but I’ve actually researched and measured this stuff – all in the name of science!). Likewise, when the nose is cleared, approximately 2-6cc. can emanate from each nostril. So the next time you go out running count the number of times you clear your nose or throat back to mother earth. The average sniff and spitter generates about 10cc of fluid with each episode. Clearing the nose or throat every quarter hour during a four-hour trail marathon places some 160cc of product along the race course. You might argue that 500 runners crossing Death Valley were a boon to adjacent plant life with this output! Truth is that, volume-wise, it’s not much. 160cc constitutes less than 6 ounces or the rough equivalent of an old fashioned, non-Starbucks cup of coffee. It would require only 6oz. of Gatoraid to replace the sodium, potassium, and water while the bicarbonate and protein loss is relatively minimal. Is this significant? Not very, at least not for most of us who pay close attention to estimating and replacing our losses during distance events. Yet when it comes to endurance running the less we have to remember to replace the better our outcome is likely to be. Unlike replacement drinks, our spit and snot is “us”. We don’t have to figure out those losses if we don’t loose them in the first place.

So the bottom line is that it is not just good etiquette to avoid spitting and clearing our noses while running, it is also a sound physiological act to swallow those vital body fluids and retain as much personal water, protein, and electrolyte as possible. If it feels better to externally clear your system, be sure to pull in a few extra ounces of fluid to account for it. But if you find it annoying, and there is someone in your training group that annoys you with their constant spitting or nose clearing, send them this article.

(Author Dr. Larry Dunlap is a runner and Emergency Medicine physician; he also happens to be my dad!)