A kidney infection usually feels like a bad flu and a UTI rolled into one, with a deep, often sharp pain in your side or back near the kidneys.

What does a kidney infection feel like?

A kidney infection (also called pyelonephritis) is a serious urinary tract infection that has moved up into one or both kidneys. It usually comes on quickly over hours to a day or two.

The “overall” body feeling

Many people describe it like having the worst flu plus intense back pain:

  • Sudden fever (often high) and chills or shivering.
  • Feeling very unwell, washed out, or “poisoned,” not just a bit off.
  • Aching muscles and fatigue, wanting to stay in bed.
  • Loss of appetite, sometimes weight loss if it goes on.

An example: someone might feel fine in the morning, then by afternoon develop a 38–39°C+ fever, chills, and feel like they’ve been “hit by a truck,” with pain in one side of their back.

The pain: where and what it feels like

The pain is one of the main clues that it’s gone beyond a simple bladder infection.

  • Pain in your side , lower back, or flank (under the ribs, usually one side, near the kidney).
  • It can spread toward the groin or lower belly.
  • It may be dull and throbbing, or sharp and severe, and usually does not improve just by changing position.
  • It often feels different from typical muscle strain: it’s deeper, more “internal,” and paired with feeling sick and feverish.

Some people find it hurts more when:

  • The area is pressed or tapped.
  • They’re walking or moving around.

Pee (urine) symptoms that often come with it

A kidney infection almost always comes with urinary tract symptoms, either new or recently worse:

  • Burning or stinging when you pee.
  • Needing to pee more often and urgently, even if only a little comes out.
  • Urine that is dark, cloudy, bloody, or foul-smelling.

HTML table as requested:

html

<table>
  <thead>
    <tr>
      <th>What you might notice</th>
      <th>Typical in kidney infection?</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Burning or pain when peeing</td>
      <td>Common symptom[web:1][web:3][web:5][web:7][web:9]</td>
    </tr>
    <tr>
      <td>Need to pee very often / urgently</td>
      <td>Common, often with small amounts of urine[web:1][web:3][web:5][web:7][web:9]</td>
    </tr>
    <tr>
      <td>Cloudy, dark, or bloody urine</td>
      <td>Common; can be a warning sign[web:1][web:5][web:7][web:9]</td>
    </tr>
    <tr>
      <td>Bad-smelling urine</td>
      <td>Frequently reported[web:5][web:7][web:9]</td>
    </tr>
  </tbody>
</table>

Stomach and nausea symptoms

Because the kidneys sit near the upper part of your abdomen and the infection affects your whole body, gut symptoms are common:

  • Nausea and vomiting.
  • “Upset stomach” and sometimes diarrhoea.
  • Belly or lower abdominal pain, often on the same side as the back pain.

If vomiting is frequent or you can’t keep fluids down, that’s a red-flag situation.

What it can look like in different age groups

Kidney infection doesn’t always feel textbook, especially at the extremes of age.

In younger adults

Most classic, “typical” pictures are described in younger and middle‑aged adults:

  • Fever and chills.
  • One-sided back or side pain.
  • Strong urinary symptoms (burning, frequency, smelly or cloudy urine).

In children

Young children may not say “my kidney hurts,” so you see more general signs:

  • High fever without a clear cause.
  • Irritability, poor feeding, or poor weight gain in very young kids.
  • Sometimes vomiting or seeming generally very unwell.

In older adults

Older adults may have fewer urinary symptoms but more changes in thinking:

  • Confusion, drowsiness, “not themselves.”
  • Jumbled speech, hallucinations in some cases.
  • They might not complain of pain or burning when peeing at all.

How it differs from a simple UTI

Both are infections in the urinary tract, but a kidney infection is more serious and “higher up.”

  • Simple bladder UTI
    • Burning when peeing, frequent urge, lower pelvic discomfort.
    • Usually no high fever, no severe back pain, you still feel relatively okay overall.
  • Kidney infection
    • All or some UTI symptoms plus : high fever, chills, strong feeling of being ill, pain in side/back/groin, nausea/vomiting.
* Can develop from an untreated or recurrent UTI over time.

When it’s an emergency

Kidney infections can lead to sepsis, which is life-threatening if not treated quickly. You should seek urgent or emergency care (same day, or call emergency services) if:

  • You have kidney‑infection‑type pain plus a high fever or shaking chills.
  • You feel suddenly very weak, dizzy, or faint.
  • You have trouble breathing, racing heart, or severe pain.
  • You are confused, drowsy, or having difficulty speaking or thinking clearly.
  • You cannot keep fluids or medicines down due to vomiting.

If you’re pregnant, have diabetes, kidney disease, or a weakened immune system, any suspected kidney infection should be treated as urgent.

What to do if you think you have one

  • Get same‑day medical advice if you have flank/back pain, fever, and urinary symptoms – you usually need antibiotics and sometimes hospital care.
  • Drink fluids if you can, but don’t try to “treat it at home” alone; home remedies are not enough for kidney infections.
  • Do not delay because symptoms can escalate quickly and kidney damage or sepsis can occur if it’s left untreated.

Quick Scoop (recap)

  • A kidney infection feels like: deep one‑sided back/side pain, plus fever, chills, and a very “ill” feeling, usually with burning or urgent urination and bad‑smelling or cloudy urine.
  • It is not just a mild UTI; it is serious and needs prompt medical treatment.
  • Red flags: high fever, severe flank pain, vomiting, confusion, or feeling extremely unwell – these need urgent or emergency care.

Information gathered from public forums or data available on the internet and portrayed here.

If you or someone else currently has these symptoms, contact a doctor or urgent/ emergency service now rather than waiting to see if it passes.