All the ways running marathons can wreck your body — from ‘jogger’s nipples’ to colorectal cancer

Beating yourself up for sitting out Sunday’s TCS New York City Marathon? Don’t — your body might actually thank you.

From blistered feet and aching joints to a churning stomach and battered muscles, the iconic 26.2-mile race can wreck far more than just your ego.

“Running a marathon is an incredible physical and mental achievement, but it’s also a demanding event that places unique stresses on the body,” Dr. Mariam Zakhary, director of running medicine for Mount Sinai’s Department of Rehabilitation and Human Performance, told The Post.

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A 2024 study of more than 1,000 NYC Marathon runners found that nearly 40% were injured while preparing for the race, and roughly 14% got hurt on the course.

Many of these injuries stem from overuse or training errors, which Zakhary said can often be avoided with the right preparation.

The Post spoke to eight specialists to uncover the toll that running a marathon can take on the body if you aren’t careful. Spoiler alert: It isn’t pretty — whether you walk away with a medal or not.

Heel hell

“Dr. Rock G. Positano, founder and director of the Non-surgical Foot and Ankle Service and the Heel Pain Center.

The plantar fascia, which connects your heel to your toes, acts as the body’s major shock absorber. Its fat pad has a low blood supply, he explained.

“The marathon stress can accelerate degeneration of the fascia and lead to partial and, in some cases, complete tearing,” Positano said, noting that this can cause sharp, stabbing or aching pain in the heel or arch.

Cracked under pressure

Stress fractures, or tiny hairline cracks in the foot and leg bones — particularly the metatarsals, navicular and tibia — are also common in marathon runners, Positano said.

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“It may not present until a few days past the marathon,” he noted, adding that it can cause swelling and “extreme pain” when bearing weight.

Tendon trouble

“Achilles tendinopathy develops through repetitive eccentric overload, frequently exacerbated by hill running or abrupt mileage increases,” said Dr. Adam Bitterman, chair of orthopedic surgery at Huntington Hospital.

This common condition causes pain and inflammation in the Achilles tendon, which connects the calf muscle to the heel bone.

Runners with flatfoot deformities or poor shoe mechanics may experience posterior tibial tendon dysfunction, Bitterman noted.

This condition happens when the posterior tibial tendon, which runs along the inside of the ankle and foot, becomes inflamed, causing pain and sometimes making it difficult to walk.

Twist of pain

“Ankle sprains can occur on uneven terrain or in fatigued runners with diminished proprioception,” or your body’s ability to sense its own position and movements, Bitterman said.

These happen when the ligaments supporting the ankle joint are stretched or torn, leading to pain, tenderness, swelling, bruising, and difficulty walking.

Muscle mutiny

“Cramping in the calf muscles is very common, especially after miles 15-20,” Positano said.

This involuntary, painful contraction is often due to dehydration and muscle fatigue, he explained, along with electrolyte imbalances.

Toe-tal horror

Marathon runners also often suffer from subungual hematomas, or the collection of blood under the nails from repetitive trauma of the toes hitting the top of the sneaker, Positano said.

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“Blood accumulates and the nail becomes engorged and infection is right around the corner,” he explained. “It doesn’t sound too serious, but an infected nail is one of the most painful foot issues and affects walking.”

Bubble trouble

Aside from foot, ankle and leg injuries, dermatological conditions can occur with long-distance running.

“One of the most common issues is due to friction,” said Dr. Jacob Beer, board-certified dermatologist. “At longer distances, such as a marathon, runners can experience friction blisters on their feet.”

This can happen to anyone, but he said it’s made worse by poor-fitting shoes or by wearing socks that aren’t moisture-wicking. Over time, runners tend to develop calluses on their feet, which can help prevent blistering.

Rubbed the wrong way

But friction injuries aren’t just a problem for your feet.

“Another common area is on the nipples,” Beer said, noting that this is often called “jogger’s nipple,” caused by friction between the nipples and clothing during prolonged or intense exercise, particularly in men.

The inner thighs, underarms, waistband, between the toes, and sports bra area are also prime areas for chafing.

Fungal frenzy

“Superficial fungal infections, such as tinea pedis or athlete’s foot, are also very common,” Beer said.

“This is because the fungi love the moist environment of the feet and adding more warmth and sweat makes it even more hospitable to them,” he explained.

The combination of sweat, friction, and clothing can also lead runners to develop hair follicle infections called folliculitis, especially in the groin or buttock areas.

Scorched and soaked

Long-distance runners also need to watch out for sunburn and other hazards from prolonged exposure to the elements.

“Environmental factors such as heat, humidity, and UV exposure further compromise and injure the skin barrier, making it more vulnerable to irritation and injury during or after a marathon,” said Dr. Jonathan Ungar, medical director for the Waldman Melanoma & Skin Cancer Center at Mount Sinai Health System.

That can lead to problems like heat rash, or the red, itchy bumps that tend to appear on the back or chest.

Trots and tribulations

Skin problems aside, several gastrointestinal issues can affect marathon participants, including diarrhea, often called “Dr. Dana Zalkin, a gastroenterologist and assistant professor of medicine at the Icahn School of Medicine at Mount Sinai.

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“During a race, blood flow is shunted away from organs like your stomach and gut and directed toward the active tissues such as your muscles, heart, lungs, and brain,” she explained. “This decrease in blood flow can irritate the gut and cause diarrhea. Dehydration can exacerbate this issue as well.”

Gut check

The mechanical jostling that occurs while running is also thought to lead to other gastrointestinal symptoms, Zalkin said.

“The repetitive motion of moving up and down can irritate the organs in the abdomen and cause symptoms such as nausea, abdominal cramping and the urge to defecate,” she explained.

Heartburn havoc

Running a marathon can also worsen acid reflux, either during or after the race, noted Dr. Jeremy Polman, a gastroenterology fellow at Northwell’s Lenox Hill Hospital.

This is also caused by the mechanical jostling in the stomach and reduced blood flow to the digestive system, along with increased intra-abdominal pressure and heavy breathing.

Defenses down

Research shows that the immune system can weaken for 3 to 72 hours after a marathon because of the significant demand that the race places on the body.

This increases susceptibility to infections and illness, with many marathoners coming down with colds or fevers following a race.

Brain drain

A 2025 study found that marathon running can cause a temporary reduction in brain myelin, the fatty insulating layer around nerve fibers.

Fortunately, it typically recovers within about two months. Researchers believe this happens because the brain may use myelin as an energy source once other fuel reserves are depleted.

Overworked organs

Marathon runners may also sustain acute kidney injuries during the race. However, research suggests that most recover fairly quickly and don’t suffer long-term damage.

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Muscle meltdown

There are also some rare but serious medical complications that can arise from running a marathon.

Rhabdomyolysis, for example, is a life-threatening injury that happens when the muscles start break down, ushering a protein called myoglobin and other components into the bloodstream.

This can turn urine brain and lead to serious kidney damage. It’s uncommon for endurance runners, and when it does occur, it’s usually tied to dehydration or a prior illness.

Water woes

Over-hydration during a marathon can trigger hyponatremia, a dangerous condition caused by a drop in blood sodium levels due to diluting the blood with too much fluid.

Symptoms include confusion, nausea and swelling — and, in severe cases, it can be fatal.

Cardio complications

Though rare, some runners have experienced acute coronary events during marathon training. In most cases, underlying health issues play a role.

“All patients should undergo pre-marathon health screening with their physician,” said Dr. Gina LaRocca, a cardiologist at Mount Sinai Fuster Heart Hospital.

The big “C”

Perhaps most frighteningly, marathon running might increase your risk of colorectal cancer.

In a 2025 study of 100 people aged 35 to 50 who’d completed at least two ultramarathons or five standard marathons, researchers found that nearly half the participants had precancerous growths known as polyps.

Roughly 15% also had advanced adenomas — a type of large or unusual polyp that, while benign, carries a higher risk of turning into cancer — far above the 1%–2% normally seen in average-risk adults their age.

“The findings suggest that extreme endurance training (like running a marathon) may create unique stress on the gut that could increase the risk of advanced precancerous polyps in some athletes,” said Dr. Nicholas Hornstein, a medical oncologist at Northwell’s Manhattan Eye, Ear and Throat Hospital.

But don’t let that scare you off exercise entirely: “For most people, regular exercise is highly protective, and the key message is moderation, not fear.”