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Why Do UTIs Cause Frequent, Painful Urination? Mouse Study Offers Insight

By Dennis Thompson HealthDay Reporter

Medically reviewed by Carmen Pope, BPharm. Last updated on Aug 19, 2025.

TUESDAY, Aug. 19, 2025 — Urinary tract infections tend to be extremely painful and disruptive, prompting sufferers to urinate more frequently with a horrible burning sensation.

But a new mouse study has shed some light on why UTIs cause frequent and painful urination, the first step to creating a treatment for these symptoms.

UTI infections appear to affect nerves in the bladder that signal to the brain it’s time to go, researchers recently reported in the journal Brain, Behavior & Immunity-Health.

“UTIs cause the nerves in the bladder to become overly sensitive, which means that even when the bladder is only partly filled, it can trigger painful bladder sensations that would signal for the need to urinate,” Dr. Luke Grundy, head of neuro-urology research at Flinders University in Australia, said in a news release.

“Theoretically, we should be able to find a way to address hypersensitive nerves in the bladder and reduce or eliminate the painful and debilitating symptoms of a UTI,” Grundy added.

UTIs are one of the most prevalent bacterial infections around the world, with more than 400 million cases reported every year, researchers said in background notes. Nearly 1 in 3 women will experience a UTI before age 24.

To figure out why these infections cause an extremely painful and frequent urge to urinate, researchers studied female lab mice with UTIs caused by E. coli.

Normally, bladders expand to store urine, holding in humans as much as two cups of urine for several hours, researchers said. Once full, nerves in the bladder signal that it’s time to go seek relief.

But the bladder nerves in the mice with UTIs had been sensitized by their infection, lab results show.

“We found that UTIs, caused by bacterial infections such as E. coli, can significantly alter the function and sensitivity of the nerves that usually detect bladder fullness, a phenomenon known as ‘bladder afferent hypersensitivity,’ ” Grundy said.

The affected nerves send signals that it’s time to go even if the bladder is nowhere near full, right when the person’s infection also is making urination painful, researchers said.

“We think that these heightened sensory responses may serve as a protective mechanism, alerting the body to the infection and prompting more frequent urination to expel the bacteria,” Grundy said.

It’s likely that some drug could be used to calm the bladder nerves down, reducing the need to urinate while antibiotics wipe out the infection, he said.

Researchers next plan to explore treatments that might help soothe bladder nerves affected by UTIs.

Disclaimer: Statistical data in medical articles provide general trends and do not pertain to individuals. Individual factors can vary greatly. Always seek personalized medical advice for individual healthcare decisions.

© 2025 HealthDay. All rights reserved.

Posted August 2025

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