How Can You Get A Kidney Infection Causes Risks?

A kidney infection is a serious type of urinary tract infection that starts in your bladder or urethra and moves up to one or both of your kidneys. You get it when bacteria, most often E. coli from your own digestive tract, travel up the ureters and into the kidney tissue. The main risk factors include being female, having a blockage like a kidney stone, using a catheter, or having a condition that weakens your immune system. These infections require prompt medical treatment with antibiotics to prevent permanent kidney damage or a life-threatening blood infection.

What exactly causes a kidney infection?

Bacteria cause nearly all kidney infections. The most common culprit is Escherichia coli, or E. coli, which normally lives in your intestines without causing harm. The trouble starts when E. coli gets into your urinary tract through the urethra and multiplies in the bladder.

From the bladder, the bacteria can travel up the ureters — the tubes that connect your bladder to your kidneys. Once they reach the kidney tissue, the immune system responds with inflammation. That inflammation is what causes the fever, back pain, and nausea you feel.

Less common causes include other bacteria like Klebsiella or Proteus, and in rare cases, a fungal infection. Current research suggests that about 90 percent of uncomplicated kidney infections are caused by E. coli.

How can you get a kidney infection from a bladder infection?

A kidney infection is almost always the result of an untreated or undertreated bladder infection. When bacteria stay in the bladder long enough, they can multiply and travel upward. This is why doctors take urinary tract infections seriously — especially in women, children, and older adults.

Not every bladder infection becomes a kidney infection. But the risk increases if you delay treatment, if the bacteria are resistant to the antibiotic you take, or if you have a structural problem in your urinary tract that makes it easier for bacteria to climb up.

Some people report that they had no bladder symptoms before their kidney infection started. This is possible, though less common. The infection can move quickly, especially in people with weakened immune systems.

What are the biggest risk factors for getting a kidney infection?

Being female is the single biggest risk factor. Women have a shorter urethra than men, which makes it easier for bacteria to reach the bladder. Pregnancy also increases risk because hormonal changes slow the flow of urine through the ureters.

Blockages in the urinary tract are another major risk. Kidney stones are the most common blockage. When urine cannot flow freely, bacteria have more time to multiply and travel upward. An enlarged prostate in men can also block urine flow and increase risk.

Other significant risk factors include:

• Using a urinary catheter, which can introduce bacteria directly into the bladder
• Having diabetes, which weakens the immune system and can damage nerves that control urination
• Having a condition that causes urine to flow backward from the bladder to the kidneys, called vesicoureteral reflux
• Having a weakened immune system from medications like chemotherapy or from conditions like HIV

As of 2026, studies have also found that frequent antibiotic use can increase risk by promoting resistant bacteria. This does not mean you should avoid antibiotics when you need them. But it is a reason to use them only when prescribed.

How can you tell the difference between a bladder infection and a kidney infection?

A bladder infection usually causes pain or burning when you urinate, a frequent urge to go, and cloudy or strong-smelling urine. A kidney infection adds symptoms that affect your whole body: fever, chills, nausea, vomiting, and pain in your upper back or side, just below the ribs.

If you have a fever higher than 101 degrees Fahrenheit along with urinary symptoms, that is a strong sign the infection has reached your kidneys. The back pain from a kidney infection is usually on one side and stays constant rather than coming and going.

Some people also feel confused or disoriented, especially older adults. This is a serious sign that the infection may be affecting the whole body, a condition called urosepsis.

Here is a quick comparison of typical symptoms:

Does having a kidney stone directly cause a kidney infection?

A kidney stone does not cause an infection by itself. But it creates the perfect conditions for one to develop. Stones block the flow of urine, and stagnant urine is a breeding ground for bacteria. Even a small stone that partially blocks a ureter can increase your risk significantly.

Some stones are also made of materials that bacteria can cling to. Struvite stones, in particular, are directly linked to certain types of bacterial infections. These stones can grow quickly and fill the inside of the kidney, making them hard to remove and increasing the chance of repeat infections.

If you have a kidney stone and develop a fever with back pain, that is a medical emergency. The combination of a blocked ureter and an infection can damage the kidney permanently within hours.

Can you get a kidney infection from sexual activity?

Sexual activity can increase the risk of a kidney infection, but it does not cause it directly. The bacteria that cause most kidney infections come from your own body, not from a partner. During sex, bacteria from the genital area can be pushed into the urethra, where they can travel to the bladder and eventually to the kidneys.

Women who are sexually active have a higher rate of urinary tract infections overall. Using a diaphragm or spermicide also increases risk because these can change the normal balance of bacteria in the vagina. Urinating soon after sex helps flush bacteria out of the urethra before they have time to multiply.

This is widely claimed though strong evidence is limited for some specific sexual practices increasing kidney infection risk directly. What the research does show clearly is that any activity that introduces bacteria into the urethra raises the risk of a bladder infection, which can then become a kidney infection.

What should you avoid if you think you have a kidney infection?

Do not wait to see if symptoms go away on their own. Kidney infections do not resolve without antibiotics. Delaying treatment gives the bacteria more time to multiply and spread into your bloodstream.

Do not rely on cranberry juice or other home remedies. Cranberry products may help prevent bladder infections in some people, but there is no evidence they can treat an active kidney infection. You need prescription antibiotics.

Do not take leftover antibiotics from a previous illness. The bacteria causing your current infection may be resistant to that specific drug. Taking the wrong antibiotic can make the infection worse by killing weaker bacteria while allowing resistant strains to thrive.

Do not take ibuprofen or aspirin for the fever without checking with your doctor. Some studies suggest that anti-inflammatory drugs may interfere with your body’s ability to fight the infection, though the evidence is not yet conclusive. Acetaminophen is generally considered safer for fever in this situation.