In my opinion, there’s nothing more gross than being right behind a runner who decides to launch a mouthful of spit into the air. Thankfully I’ve never been hit by a spit rocket but I know people have. Why does running make you need to spit?

Complete disclaimer here – there have been times when I’ve been in the middle of nowhere, on a country lane, and decided the best way to get rid of the thick mucous in my mouth would be to spit it into the hedgerow. I would never do this when anyone else was around and particularly if there was a risk of hitting them with it!

I decided to research this to find out why our body creates more saliva when we run and why it is that that spit seems to be thicker and harder to swallow.

Why do we make saliva?

Saliva is made in our salivary glands. We have three pairs of salivary glands:

  • Sublingual – underneath our tongue
  • Submandibular – tucked under our jaw bone
  • Parotid – just in front of our ears

Saliva has a few different functions:

  • It helps to keep germs out
  • It keeps our mouth and tongue moist – this helps with talking as well as making it feel comfortable
  • It protects our dental hygiene
  • It moistens food to make a nice food bolus to swallow
  • It starts the process of digestion

Saliva is 99 per cent water. It also contains electrolytes, mucous cells, immunoglobulins, enzymes and proteins.

The production of saliva is controlled by our nervous system – both the sympathetic and the parasympathetic systems.

Saliva and running

When you sit down to a nice meal and start tucking in, your parasympathetic nervous system is triggered. This is your relaxed state. Saliva flow increases in amount and it’s nice and watery to help chew and digest food, the protein content is low.

When you exercise, your sympathetic nervous system kicks in. The flow of saliva may increase but it also increases in thickness and stickiness. This is what can make it hard to swallow and drives runners to spit it out. The thickness increases for three reasons:

  1. Protein release. Exercise, of any intensity, increases the production of certain salivary proteins including one called MUC5B which increases in amount immediately after exercise. When protein concentration of saliva is increased it makes it thicker. Think of it as having more gravy powder in your jug of hot water.
  2. Dehydration. If you become dehydrated, your body wants to preserve water wherever it can. Reducing the water content of saliva is a good way to do this. Saliva thickens as a result and it can leave you with a sticky yet dry mouth. You have the same amount of gravy powder but less water.
  3. Mouth breathing. Most runners breathe through their mouths, especially during higher intensity exercise. Your body wants to keep your mouth moist and because the air is drying it out, the glands produce more saliva. However the saliva that it there is thicker because the water content reduces by evaporation. It’s also possible that cold air could have a direct effect on the salivary glands causing them to excrete more mucous too.

What can we do about spitting and running

There’s no easy answer here. We’re all different, we all produce varying amounts and thickness of saliva when we run. Sipping water frequently can help stop your mouth drying out and reduce salivary thickness. Otherwise it’s up to you whether you think it’s socially acceptable to spit it out in public, especially in this age of Covid when we need to keep our respiratory secretions to ourselves. Spitting into a tissue and finding a bin is an alternative option.

Is thick spit when running something you struggle with? Do you think it’s ok to spit it out whenever you are? I know this can be a controversial topic so I look forward to your comments here on the blog and on social media!

There are other tips like these, including how to cope with the acid taste you can get in your mouth when you run in my new book Run Well: Essential health questions and answers for runners. Published by Bloomsbury and available to buy now. 

Featured image: athree23 from Pixabay

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2 Comments

  1. I always try to find a sewer grate, or area of bushes/non-trampleable ground to spit into, or a swig of water to dilute and then swallow it sometimes.

    I do favour the spit method where its not too crowded and I can find a space

    1. Sometimes swallowing means you take in air which I find uncomfortable when I’m running. Lucky I live in the country. I’ve never spat in a race however much I’ve wanted to!

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