In addition to bacteria from your own stool travelling up the urethra, there are other known causes of UTI:
Sexual intercourse - Regular sexual intercourse can sometimes predispose women to urinary tract infections.
The reason for this is quite simple: a woman's urethra is very close to the anus and perineum, which are notorious for harboring stool-borne bacteria.
During sexual intercourse, bacteria from these areas may reach the urethra. A woman's urethra is much shorter than the male urethra, which explains why women have a higher risk for UTI than males.
Catheterization - Catheters are tubes inserted through the urethra and into the bladder to allow urine to be collected in a bag or bottle. Catheterization is often performed in hospitals and critical care facilities when a patient is unable to regularly urinate by himself.
Both males and females can undergo catheterization. Long-term use of this method of draining urine can increase the risk of developing UTI, even while a person is still in the hospital.
Blood-borne or lymph-borne bacteria - Bacteria present in the bloodstream, and those that have passed through the lymph nodes, can sometimes infect the urinary tract from within. The symptoms of such an infection are the same, and the conventional treatment is similar, if not completely identical, to UTI originating from urethral infection.
Physical abnormalities and diseases of the urinary tract - Lumps, nodules, tears along the urinary tract, and enlargement of organs that are connected, or are part of the renal system, can also cause urinary tract infections.
If you have an enlarged prostate, you are at higher risk for UTI. Bladder problems can also arise if you are a chronic smoker/tobacco user. Structural issues within the body can predispose a person to urinary tract infections, because the body is unable to fully eliminate urine when it needs to.
When there is a build-up of urine in the body, bacteria that should have been eliminated from the urinary tract is trapped and may proliferate, causing infection from within.
Clothing material - Not all clothing materials are created equal. Some undergarments may look sophisticated and sexy, but they may cause urinary tract infections if it turns out that they are not manufactured with cotton (or mostly cotton).
Many clothing brands nowadays manufacture clothes with a mix of polyester/nylon and cotton. Cotton is usually not the base material, because it's more expensive.
Clothes such as panties, lady briefs, boxer shorts, and briefs that are made from 100% pure cotton are often the most expensive (which explains the demand for less pricey brands that make use of little or no cotton at all).
If you buy "no-cotton" undergarments most of the time, it is worth noting that such undergarments are hotbeds for urinary tract infections, because they make the genital area warmer and more moist than usual.
A warm and wet environment is the ideal place for different kinds of bacteria to grow - including pathogens that cause urinary tract infections.
Why does this happen in the first place? The problem lies in airflow. Cotton undergarments naturally let more air in, allowing your genital area, and your undergarment, to dry more quickly.
Cotton also wicks away moisture from the genital area, keeping it even drier. Non-cotton undergarments absorb only a very small quantity of moisture, and leave the rest to remain on the surface of the skin, promoting bacterial growth.
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