A kidney infection typically feels like a deep, persistent ache on one side of your back, between your lower ribs and hip. Unlike a simple bladder infection that stays “down low,” a kidney infection sends pain higher up and brings whole-body symptoms like fever, chills, and nausea that can make you feel genuinely sick. Understanding exactly where and how those sensations show up helps you distinguish a kidney infection from other causes of back or abdominal pain.
Where the Pain Shows Up
The hallmark sensation is flank pain, felt in the area on either side of your spine between the bottom of your ribcage and the top of your hip. Most people describe it as a deep, dull ache rather than a sharp, stabbing pain, though it can range anywhere on that spectrum. It usually affects only one side, since kidney infections most often develop in a single kidney.
One useful clue: kidney pain generally does not get worse when you move, bend, or twist. That separates it from a pulled muscle or spinal problem, which tends to flare with certain positions. Instead, kidney infection pain stays relatively constant and may intensify if someone presses or taps the area on your back just below the ribs. That spot, called the costovertebral angle, is exactly where doctors check during an exam. A sharp wince when they tap there is one of the strongest physical signs pointing toward a kidney problem.
Some people also feel pain wrapping around to the lower abdomen or radiating down toward the groin, which can make it easy to confuse with a stomach issue or a kidney stone. The key difference is that a kidney infection almost always comes with fever and urinary symptoms on top of the pain.
Urinary Symptoms That Accompany It
Because kidney infections usually start as bladder infections that travel upward, you’ll often notice lower urinary tract symptoms first or alongside the flank pain. These include a burning sensation when you urinate, a frequent and urgent need to go (even when little comes out), and pressure or discomfort just above your pubic bone.
Your urine itself may look different. Cloudiness is common, and you might notice a stronger, more unpleasant smell than usual. Some people see pink, red, or brownish urine, a sign of blood in the urine. That color change can look alarming, but it takes only a tiny amount of blood to tint urine noticeably. Visible blood doesn’t automatically mean an emergency, but combined with back pain and fever, it strongly suggests the infection has reached the kidneys.
Fever, Chills, and Feeling “Whole-Body Sick”
This is the biggest difference between a bladder infection and a kidney infection. A simple UTI rarely causes a fever. A kidney infection frequently does, often accompanied by shaking chills that feel like you can’t get warm no matter how many blankets you pile on. Some people swing between intense chills and sweating as their temperature fluctuates.
Nausea and vomiting are also common. The kidneys sit near many of the same nerve pathways that serve the stomach, so a kidney infection can trigger significant gastrointestinal upset. You might lose your appetite entirely, feel waves of nausea, or actually vomit. Combined with the fatigue that comes with fighting any serious infection, many people describe the overall experience as flu-like, except the pain clearly centers on one side of the back.
How It Differs From a Kidney Stone
Kidney stones and kidney infections can produce pain in the same general area, and sometimes a stone causes an infection by blocking urine flow. But the pain quality tends to be different. Stone pain is usually intense and wave-like, spiking and easing in cycles as the stone shifts. It often radiates from the back down into the groin or inner thigh, and people typically can’t find a comfortable position.
Kidney infection pain is more steady. It sits in the flank and doesn’t tend to move around as dramatically. And while a stone can exist without a fever, a kidney infection almost always produces one. If you have both severe colicky pain and a fever, that combination raises concern for a stone that has led to infection, which needs prompt medical attention.
Symptoms in Older Adults Can Look Different
In adults over 65, a kidney infection may not follow the textbook script at all. The burning during urination that younger people notice might be absent, because the immune response shifts with age. Instead, the earliest signs can be confusion, increased agitation, new incontinence, loss of appetite, or falls. For someone with Alzheimer’s disease or dementia, a urinary tract infection can temporarily worsen cognitive symptoms, which caregivers sometimes mistake for disease progression rather than an infection.
Any sudden change in mental clarity or behavior in an older adult, especially if paired with a low-grade fever or new difficulty urinating, warrants a urine test to check for infection.
Warning Signs That Need Emergency Care
Most kidney infections are treatable and resolve with antibiotics. But in some cases the infection enters the bloodstream, a condition called urosepsis, which is a medical emergency. The signs that a kidney infection is becoming dangerous include a rapid heart rate or palpitations, difficulty breathing or a respiratory rate faster than about 22 breaths per minute, a weak pulse, and blood pressure dropping noticeably (a top number below 100). You might feel lightheaded, confused, or unable to urinate at all.
If you started with typical kidney infection symptoms and then develop any of those signs, or if you feel like you’re getting significantly worse rather than better, that shift suggests the infection is overwhelming your body’s ability to contain it. This is the point where getting to an emergency room matters more than waiting for a scheduled appointment.