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 UTIs 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.  In the vast majority of cases a 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 usually without more severe symptoms.

A fraction of cases can turn into a reccurring or chronic UTI, which is then called a complicated UTI.  Complicated UTIs 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 cause a life-endangering kidney infection. The symptoms of the latter include high fever and chills, back or flank pain, nausea and vomiting

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: limited to approximately 2% of all complicated UTIs.

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What can cause a UTI?

UTIs are caused by bacteria getting into the urinary tract that have no business being there.  The most common bacteria family to trigger UTIs is E. coli, which normally resides in the digestive tracts and is therefore found in 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, infection ensues.  Risk factors that raise the likelihood of bacteria entering the urinary tract include:

  • Being a woman: women have shorter urethras, 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.  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 of bacterial infections in the urinary tract. 
  • Pregnancy: UTIs occur more commonly during pregnancy, since the enlarged uterus can weigh on the bladder and thereby inhibits the bladder from emptying out completely.  Any pregnancy-related UTI is categorized as a complicated UTI because, if untreated, it can be 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 UTIs more frequently and more severely increases.  There’s also a higher likelihood that the infection can advance to the kidneys.  Controlling glucose levels is therefore, crucial in preventing and managing UTIs.  Talk to your endocrinologist or primary MD about improvung your diabetic management.
  • Weak immune system: I you have preexisting autoimmune issues, such as cancer or HIV, or if you are post menopausal, your immune system probably is weaker than that of a young, healthy person.  This may be why the risk of developing a UTI increases with advanced age.  UTIs in older women can also be more difficult to treat.

What can I do to prevent a UTI?

Good genital hygiene is of paramount importance if you want to minimize the risk of getting a 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 as they can cause skin rashes and increase the risk of infection.  

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, or rinse off and use a new condom.  Urinating after sex helps to flush bacteria you may have contracted during sex out of your system.  Avoid sexual intercourse when you are not well lubricated.  “Dry” sex can cause friction and abrade the urethra making you prone to bacterial infection.  You can use lubricants or lubricated condoms to avoid this. 

Make sure not to wear tight underwear and/or pants, especially during the summer months.  Warm and moist environments are ideal for bacterial growth.  Often the problem is not the underwear but the tight jeans you are wearing on top of it.  Avoiding synthetic underwear also helps.

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 flush out your urinary tract and stop bacteria from colonizing.

Keep the above in mind, and you have a good chance of preventing a 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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