What Causes A Bloody Or Metallic Taste In Your Mouth During Intense Exercise?

blood taste in mouth during exercise

If you are a runner, cyclist, or other endurance athlete, you more than likely have had a bloody metallic taste in your mouth; especially during intense exercise. I would also guess you’re curious why that happens.

The bad news is no one knows the exact cause. The good news is this bloody taste is entirely harmless.

In this article, we’ll take a look at the theories as to why this bloody taste happens and what you can do to prevent it from happening to you.

Theory #1: The Bloody Taste In Your Mouth Is Due To Alveoli Breaking

Quick physiology lesson. When you exercise, especially at a high intensity, your heart rate and blood pressure increase. These two things happen because your heart needs to pump more oxygen-rich blood to keep your muscles working. This blood also needs to be pumped through your lungs to get that oxygen.

When you’re sucking wind during an intense workout, you take big gulps of O2 that moves down your trachea (windpipe), to the bronchioles, and finally, the oxygen arrives at the tiniest sacs in the lungs. The alveoli.

The alveoli are fragile little things (very thin and porous), and the increase in blood pressure with intense exercise can make them burst and leak out blood (hemoglobin), which happens to be iron-rich.

Some of the blood from the broken alveoli is sent through the bronchi to your mouth. Once it reaches our mouth, the iron molecules from the blood come in contact with receptors on the tongue that are sensitive to iron.

These receptors then communicate a message to the brain that we sense a bloody or metallic taste in our mouth.

Theory #2: Salivary Duct Stones Cause the Metallic Or Blood Taste

As odd as this one sounds, this is one of the more generally accepted theories that goes like this. Just as you can get kidney stones, you can also develop stones in your salivary ducts. This can cause a blockage and/or infection.

Intense exercise and heavy breathing can increase saliva production and this, in turn, could cause an infected salivary duct to give off a bloody or metallic taste.

Other Theories

Outside the two most generally accepted theories described above, there may also be a few other culprits that cause the bloody, metallic taste in your mouth during exercise. These are:

  1. Cracks in the lining of your throat and nose that leak small amounts of blood could be to blame. Especially if you are exercising at altitude or in the cold, dry air.
  2. Increased pressure on the lungs from intense exercise may cause hemoglobin to leak into air sacs.
  3. Pulmonary swelling that is caused by fluid leaking into the spaces between air sacs and capillaries.
  4. Tooth decay.
  5. Mucous membranes in your mouth dry out from dehydration.
  6. Stomach regurgitation.

Now that we know what may cause this bloody taste in your mouth during exercise let’s discuss how to prevent it.

How To Stop The Bloody/Metallic Taste In Your Mouth

Nine out of ten times people get the bloody taste in their mouths because they have been sedentary and start their exercise program with a hard cardio session or running.

Translation: You are not fit, and you are pushing too hard out of the gates.

Instead, if you intend to start endurance exercise begin with low-intensity workouts. Think 65-70% of maximum heart rate. This will allow the blood vessels to grow stronger and eventually handle the high pressure of more intense cardio sessions.

If you’re already fit and still experiencing the “blood in your mouth” taste make sure you are warming up 10-15 minutes before you put the pedal to the metal during hard workouts or races.

The increase in body temperature from the warm-up will help arteries expand and allow oxygen-rich blood to flow more freely to muscles.

If the above recommendations don’t solve the problem you should consult your doctor to rule out other more serious causes.

About the author:

Matt Mosman (MS, CISSN, CSCS) is a research scientist, endurance athlete, and the founder and Chief Endurance Officer at EndurElite. Matt holds his B.S. in Exercise Science from Creighton University and his M.S. in Exercise Physiology from the University of California. Matt and his family reside in Spearfish South Dakota, where they enjoy running, mountain biking, camping, and all the outdoor adventures Spearfish has to offer.