Why You Sometimes Taste Blood or Get Brain Fog While You’re Running


The benefits of aerobic exercises such as cycling or running are unmistakable. But a few of the odder side effects—like tasting blood during a race, maybe—could be mistaken for symptoms of problems.

Relax: Strange as these physiological reactions to exercise are, they generally aren’t cause for alarm, says New York City-based sports medicine doctor Jordan Metzl, M.D., author of The Athlete’s Book of Home Remedies. “Many are signs that you’ve worked your body hard,” he says. “Others are temporary issues you can generally easily address.”

Here are six strange side effects that can occur after any hard workout:

1. A Nagging Cough
You cross the line of a 5K or half marathon and walk around with a nagging cough for several minutes afterward. Blame bronchoconstriction: It’s similar to what happens in people with asthma, but it can happen to anyone.

“Exercise-induced bronchoconstriction can happen when you exert yourself at a much harder level than you’re used to,” says Metzl. “The small muscles lining your lungs get a spasm. You see it more in the beginning or end of the year when people may not be in peak shape.” Some people are also simply more genetically prone to getting it.
It’s also more common when you’re running in cold and/or dry conditions because your airways have to work harder to humidify the air as it heads into your lungs and they can get dehydrated and irritated, which leads to constriction and that cough. Breathing through a light scarf can help.

2. Metallic Taste
You’re hammering up the final hill in your local 10K and you taste blood in the back of your throat. Those are your red blood cells popping, says Metzl.

“When you push yourself past threshold, your red blood cells are being taxed and release some heme,” or iron, which is why it tastes like metal, he says. Red blood cells can also leak into your air sacs during really hard efforts. If it’s temporary, it’s nothing to worry about. (If you always taste blood, you should see your doctor to rule out underlying health issues such as infections.)

3. Runny Nose
Is your nose running? Better catch it! Yeah… Not so funny when every time you go for a run, you’re launching more snot-rockets than NASA.

It tends to get worse in the cold, but exercise-induced rhinitis (i.e. runny nose during exercise) is a common complaint among anyone who does aerobic exercises outside, especially, of course, during times when allergens like pollen, dust, and dry air are high. Your nasal passages get irritated and mucus production ensues. Interestingly, some scientists believe that air pollution, particularly the nitrogen dioxide found in car exhaust, is a big trigger—which explains why you may find yourself dripping like a faucet outside, but not on the treadmill.

If your drippy schnoz is really disruptive, you can ask your doctor about a prescription nasal spray (or grab a non-prescription remedy like Pursoma Sea Spray Nasal Rinse, which we endorse). But otherwise, just launch away.

4. You Need a Bathroom… NOW
Sometimes, especially in advance of a big race, you may have trouble making yourself poop, but the sudden, urgent need to go is more common in runners because of the inner jarring mechanics involved in running.

But any time you’re throwing back a lot of sugary foods, and there’s not a lot of blood flow through the gut to manage digestion, you’re risking trouble. That caffeine habit doesn’t help. You can ease the situation by tweaking your eating habits toward more real foods like rice cakes and bananas, downing the concentrated energy foods sparingly, and maybe sticking to a single espresso.

5. Mad Itching
Three minutes into a run, your thighs start itching like crazy. In some cases, it’s just dry skin or a natural response to warming up as your capillaries and arteries [as they] rapidly expand and stimulate nearby nerves.

But for some people, it’s an actual allergic reaction known as exercise-induced urticaria, which can cause itching and flushing, as well as hives and—in extreme cases—breathing difficulty. If you have more severe symptoms, your doctor can prescribe epinephrine, but that can cause unpleasant side effects like fatigue, weakness, and heartbeat irregularities. If it’s just itching, keep your skin moisturized, warm up gradually, and scratch as needed.

6. Brain Fog
You wrap up a long run and can’t figure out where you parked the car… or what your car looks like… or whether you even drove there in the first place.

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