Asked by: John Farrugia, Qormi, Malta

Several studies have shown that exercise increases the amount of protein secreted into the saliva, especially a kind of mucus called MUC5B. This mucus makes the saliva thicker, which makes it harder to swallow, so we spit it out. It isn’t clear why we produce more MUC5B when exercising, but it may be because we breathe through our mouth more, so the mucus stops the mouth from drying out.

Some sports, such as basketball and tennis, penalise players for spitting, but football and rugby don’t, so the players are free to expectorate!

Read more:

Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun facts.

Authors

luis villazon
Luis VillazonQ&A expert

Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.

Sponsored Deals

BBC Science Focus Magazine Subscription Offer

May Half Price Sale

  • Save up to 52% when you subscribe to BBC Science Focus Magazine.
  • Risk - free offer! Cancel at any time when you subscribe via Direct Debit.
  • FREE UK delivery.
  • Stay up to date with the latest developments in the worlds of science and technology.
SUBSCRIBE NOW