What are the causes of urinary tract infections (UTIs)?

A practical guide to the causes of UTIs and what you can do to prevent them


What is a UTI?

UTI is one of the most common infections globally, with around 150 million cases occurring every year. More than 90% of people who get UTI are women and it’s most often seen in the 16-35 age range. That said, women that are experiencing menopause or are in their 60s or older are also at an increased risk, simply because the immune system tends to be a bit weaker at that age. In the vast majority of cases, UTI is a simple acute bladder infection (cystitis) caused by bacteria and treatable with antibiotics. It can be painful and there’s an increased urge to urinate, but there aren’t any more severe symptoms.

A fraction of cases can turn into a reoccurring or chronic UTI, which then is called a complicated UTI. Complicated UTI also include pregnancy related UTI, UTI after surgery, UTI in women above age 60, as well as UTI in diabetic women. If neglected or not treated successfully, a complicated UTI can cause the bacteria to spread into the kidneys and thus cause a life-endangering kidney infection. The symptoms of the latter include high fever >100 degrees, back aches, vomiting, and body chills.

There are about 1.3 million complicated UTI cases in the U.S. every year and they require more than standard antibiotics for treatment. Fortunately, the death rate is very low: only 2% of all complicated UTI have a fatal ending.

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What things can cause a UTI?

UTIs are caused by bacteria getting into the urinary tract that have no business there. The most common bacteria family to trigger UTI is E. coli, which normally resides in the digestive tracts of animals and humans and therefore also can be found in all feces. If by accident E. coli enters the vagina and advances up the urethra (the duct that transports urine from the bladder) it can settle in the bladder and multiply. Once a certain critical mass of bacteria is reached, the bladder gets infected, causing pain and greater urination. The risk factors that raise the likelihood of bacteria entering the urinary tract include:

  • Being a woman: women have shorter urethra, which makes it easier for the bacteria to advance all the way into the bladder. Moreover, the distance between anus and the vagina’s opening, i.e., the start of the urethra, is shorter in women than the distance between anus and tip of the penis in men. So, it’s easier for bacteria from feces to contaminate the female urethra. 
  • Sexual intercourse:  The penis (theoretically even the tongue) can carry bacteria into the urethra, which is why sex hygiene is so important. In particular, going from anal sex back to vaginal sex is a big risk factor and should be avoided or at least warrant a change of condoms. Also, when you currently have a UTI, regardless of how mild or strong the symptoms are, you should avoid sexual intercourse by all means. 
  • Certain types of contraception: Diaphragms and spermicidal creams (gels that kill sperm) can increase the risk bacterial infections in the urinary tract. 
  • Pregnancy: UTI occur more commonly during pregnancy, since the enlarged uterus can weigh on the bladder and thereby inhibits the bladder from emptying out all urine. Any pregnancy UTI is categorized as a complicated UTI because it can dangerous for the mother and newborn. 
  • Diabetes: If you have diabetes mellitus and don’t manage your blood glucose levels well, the risk of getting UTI more frequently and more severely is increased. There’s also higher likelihood that the infection can advance to the kidneys. It therefore is crucial that as a diabetic person you manage blood sugar levels with great care. Your endocrinologist can support you with this and monitor your blood glucose levels.
  • Weak immune system: I you have preexisting autoimmune issues, such as cancer or HIV, or if you already are past the menopause, your immune system probably is weaker than that of a younger person. That’s why there’s an increased risk for elderly women that they’ll get UTI. It’s also more difficult to treat at older age.  

What can I do to prevent UTI?

Good genital hygiene is of paramount importance if you want to minimize the risks of getting UTI. Wash your genital area daily with a mild soap and when at the toilet always wipe from the front to the back. It’s also a good practice to rinse your genital area after each major visit to the bathroom. Don’t use hygiene sprays and creams or douches, though, as they can cause skin rashes.  

The same hygiene principles apply to sex. Always clean your genitals prior to and after sex. The same goes for your partner. Avoid swapping from anal to vaginal sex without proper cleaning and/or using a new condom. Urinating after sex helps to flush your system of any bacteria that may have gotten in during sex. Another word of caution: avoid sexual intercourse when you are not wet enough yet, as “dry” sex can cause friction to damages the urethra wall and thereby make space for bacteria to settle in. You can use lubricants or lubricated condoms to avoid this. 

Make sure to not wear tight underwear and/or pants, especially during the summer months, as the warm and moist environment in your undies is an ideal environment for bacterial growth. Often the problem is not the underwear but the tight jeans you are wearing on top of it. Also avoid synthetic underwear.

You want to stay hydrated and go to the bathroom whenever you feel like it — don’t hold your urine for too long. Frequent urination helps flushing your urinary tract and stops bacteria spread. 

If you keep the above-discussed things in mind, you have good chances for lowering your risk of getting UTI. 


  1. Kuo, Hann-Chorng, and Jia-Fong Jhang. “Recent Advances in Recurrent Urinary Tract Infection from Pathogenesis and Biomarkers to Prevention.” Tzu Chi Medical Journal, vol. 29, no. 3, 2017, p. 131,, 10.4103/tcmj.tcmj_53_17. Accessed 27 Jan. 2020.
  2. Pujades-Rodriguez, Mar, et al. “Lower Urinary Tract Infections: Management, Outcomes and Risk Factors for Antibiotic Re-Prescription in Primary Care.” EClinicalMedicine, vol. 14, Sept. 2019, pp. 23–31,, 10.1016/j.eclinm.2019.07.012. Accessed 27 Jan. 2020.
  3. Behzadi, Payam, et al. “A Survey on Urinary Tract Infections Associated with the Three Most Common Uropathogenic Bacteria.” Maedica, vol. 5, no. 2, 2010, pp. 111–5, Accessed 27 Jan. 2020.

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