Most people are familiar with the signs of an intense workout. You’re breathless and sweaty. Your heart is pounding. Your muscles are burning. But what if you start detecting a distinctive taste in your mouth: blood?

You’re not imagining it, experts say. Tasting blood during or after vigorous physical exercise is a rare but generally benign phenomenon. And it’s often simply “your body telling you that, ‘You’re probably doing a little bit more than what I’m ready to handle,’ ” said Cedric X. Bryant, president and chief science officer of the American Council on Exercise.

Reports of people noticing the bloody or metallic taste in their mouths have largely been anecdotal, with some experts noting that it appears to be more common among endurance athletes, such as distance runners, triathletes and cyclists. “There’s no pause in what they do,” said Jeffrey Lucchino, director of sports nutrition for the University of Pittsburgh Medical Center Sports Medicine. “It’s continuous, and that’s when things get more compromised in the body.”

But, Lucchino and other experts emphasized, you shouldn’t panic if you experience the off-putting taste every so often while exercising. “The good news is that it tends not to be something that people should be overly concerned about, because it tends to be a temporary phenomenon,” Bryant said. “And unless it’s associated with other more troubling symptoms, it’s really more of a nuisance byproduct of the intensity of training.”

Why do I taste blood during or after my workout?

Although this sensation has not been extensively researched, experts said, there are several scientific theories that could explain the taste, which often occurs without any visible blood.

One of the simplest reasons is that the mucous membranes of your nose and throat are irritated, said Timothy Miller, a sports medicine physician and orthopedic surgeon at Ohio State University’s Wexner Medical Center. This irritation can come from being sick and blowing your nose frequently or from working out at higher altitudes or in environments with dry or cold air. When exercising, the effort exerted on top of the existing irritation might cause the mucous membranes to “bleed just ever so slightly,” Miller said.

“That blood can leak down into the back of your throat, eventually touching your taste buds on your tongue,” he said.

Another possible cause is oral hygiene, Lucchino said. Old or loose dental fillings or tooth decay are also known to produce a metallic taste.

The “most popular theory” involves the heart and the lungs, said James Robinson, a sports medicine physician at the Hospital for Special Surgery in New York. During intense exercise, the heart can become overworked, which may lead to some fluid buildup in the small air sacs of the lungs, known as pulmonary edema, a condition commonly connected to heart problems.

In this case, experts believe that the pressure on the lungs could cause some of the red blood cells in lung tissue to “escape into the airway,” Robinson said. Red blood cells contain hemoglobin, an iron-rich protein that gives blood its metallic taste.

Exercise-induced pulmonary edema” has been documented in research, but Robinson said a proven connection between that phenomenon and the bloody taste has not been established. And although pulmonary edema is “usually a pretty scary phrase,” Miller said, “there’s a very low or very mild amount of that that takes place just from increasing intensity and effort during a workout.”

“It’s not enough to cause heart failure or anything like that,” he added, but it may be “enough to make some of those air sacs leak a little bit of blood.”

Who can be affected?

Tasting blood during or after a workout is generally associated with exercise intensity and duration as well as certain environmental conditions, Robinson said. The reason some experts think it may occur more in endurance athletes, such as distance runners, “is because of the length of the exercise,” he said. Other workouts, such as weight training, can give people more opportunities to rest and recover.

It’s possible that some people running in the upcoming Chicago and Boston marathons will notice this taste because they will be pushing themselves harder than they did in their training, Robinson said.

Your baseline fitness level could also play a role in whether you experience the taste, Miller said. It may occur more often in people who are just starting to work out or those who have suddenly dialed up the intensity of their training, he said.

Among more seasoned athletes, Miller said, “their cardiopulmonary systems are likely already essentially pre-trained to not have this condition take place unless they hit the intensity button for a workout or two a little more than even they were ready for.”

When should I seek medical care?

Noticing the taste once or twice in the early weeks of a new or adjusted workout regimen usually isn’t cause for concern, Miller said. As you get used to the exertion, you should expect to experience the sensation less often.

“If it’s doing the opposite, it’s getting more frequent or more often or more intense,” Robinson said, “that’s a little bit more concerning.”

Experts recommend being assessed by a health-care provider if the taste becomes more pronounced or occurs alongside other symptoms, such as chest pain and shortness of breath. There’s a chance the taste could be a sign of a more serious underlying condition, such as blood pressure or cardiac problems, or autoimmune issues, Miller said.

You should also seek medical attention “if you are experiencing a high volume of blood coming out of your mouth or coming out of your nasal passage during every single workout every time you push yourself,” Lucchino said.

How can I avoid this?

If you’ve been relatively sedentary and have never done regular, intense exercise, Miller suggested getting a physical exam before starting a workout program. It’s also important, he said, to help keep your mucous membranes moist by staying hydrated.

Although the bloody or metallic taste is associated with a hard workout, touting the sensation as a badge of honor is “misguided,” Bryant said. “If you’re giving yourself an appropriate dose of exercise for your level of conditioning, this isn’t something you should experience.”

Robinson agreed. Because this metallic taste could be a sign that you’re overworking your body, he said, “if anything, you should probably back off a little bit and not try to reach that point.”