Acute cystitis is a bacterial infection of the bladder, commonly called a bladder infection or lower urinary tract infection (UTI). It causes sudden-onset pain or burning during urination, a frequent and urgent need to pee, and discomfort in the lower abdomen. The infection stays confined to the bladder and doesn’t cause body-wide symptoms like fever or chills, which distinguishes it from more serious kidney infections.
Symptoms of Acute Cystitis
The hallmark symptoms are urinary frequency, urgency, and dysuria (a burning or stinging sensation when you urinate). You may feel like you constantly need to use the bathroom, only to pass a small amount of urine each time. Many people also notice pressure or discomfort just above the pubic bone.
Your urine may look cloudy or have a strong odor. Some people see pink or red-tinged urine, which means a small amount of blood is present. While alarming, blood in the urine during a bladder infection is common and typically resolves once the infection clears. What you should not have with simple cystitis is a high fever, back or flank pain, nausea, or vomiting. Those symptoms point to something more serious.
What Causes It
The vast majority of bladder infections are caused by bacteria, most often E. coli, which normally live in the digestive tract. These bacteria enter the urinary tract through the urethra and travel up to the bladder, where they attach to the bladder wall and multiply. Other bacteria can cause cystitis too, but E. coli is responsible for the largest share of cases by a wide margin.
Women get bladder infections far more often than men, largely because of anatomy. The female urethra is much shorter, so bacteria have a shorter distance to travel to reach the bladder. The urethral opening is also closer to the rectum, where gut bacteria are abundant. Sexual activity can push bacteria toward the urethra, which is why some women notice infections after intercourse. Certain contraceptive methods, particularly spermicides, can also shift the balance of protective bacteria in the vaginal area and increase risk.
Other factors that raise your chances include dehydration (less frequent urination means bacteria have more time to multiply), holding your bladder for long periods, and hormonal changes after menopause that thin the tissues of the urinary tract.
How It’s Diagnosed
For a straightforward case in an otherwise healthy woman, the combination of burning urination, frequency, and urgency is often enough for a diagnosis. A urine dipstick test can support the diagnosis by detecting signs of infection: white blood cells (which the body sends to fight bacteria) and nitrites (a byproduct certain bacteria produce). A urine culture, where the sample is sent to a lab to grow and identify bacteria, is not always necessary for simple cases but becomes important when symptoms don’t improve with treatment or when infections keep coming back.
Treatment and What to Expect
Acute uncomplicated cystitis is treated with a short course of antibiotics. The CDC recommends nitrofurantoin (typically a 5-day course) or trimethoprim-sulfamethoxazole (a 3-day course) as first-line options. Fosfomycin, given as a single dose, is another first-line choice. Stronger antibiotics like fluoroquinolones are reserved for situations where these standard options aren’t appropriate, in part to slow the development of antibiotic resistance.
Most people start feeling better within one to two days of starting antibiotics, though it’s important to finish the full course even after symptoms improve. Stopping early can leave bacteria behind and increase the chance of the infection returning or becoming resistant to treatment.
For pain relief while waiting for antibiotics to work, an over-the-counter urinary analgesic containing phenazopyridine can numb the bladder lining and take the edge off burning and urgency. The typical dose is 200 mg three times a day. This medication turns your urine bright orange, which is harmless but can stain clothing and contacts. It’s meant for short-term symptom relief, not as a substitute for antibiotics. Drinking plenty of water also helps by diluting your urine and flushing bacteria out more frequently.
How Cystitis Differs From a Kidney Infection
Acute cystitis stays in the bladder. A kidney infection, called pyelonephritis, happens when bacteria travel upward from the bladder into one or both kidneys. The key difference is how you feel overall. With cystitis, you feel uncomfortable but not truly sick. With pyelonephritis, you typically develop a fever (often above 103°F), pain in your side or back below the ribs, chills, nausea, and sometimes vomiting. You may feel generally unwell in a way that goes beyond urinary discomfort.
An untreated bladder infection can progress to a kidney infection, which is one reason prompt treatment matters. If you develop flank pain, a high fever, or begin vomiting after being diagnosed with cystitis, those are signs the infection may have spread and needs more aggressive treatment.
Recurrent Bladder Infections
Some people deal with bladder infections repeatedly. Recurrent cystitis is formally defined as three or more infections within 12 months, or two or more within six months. This is particularly common in younger women who are sexually active and in postmenopausal women.
If you fall into this pattern, a few strategies can help reduce the frequency. Urinating soon after sexual intercourse helps flush bacteria before they can establish themselves. Staying well-hydrated keeps urine flowing regularly. For postmenopausal women, vaginal estrogen therapy can restore protective bacteria and strengthen urinary tract tissues, reducing infection rates significantly. In some cases, a healthcare provider may recommend a low-dose preventive antibiotic taken daily or after intercourse to break the cycle.
Cranberry products have been widely studied, and while the evidence is mixed, some research suggests that cranberry supplements (rather than juice, which contains a lot of sugar) may offer a modest protective effect by making it harder for bacteria to stick to the bladder wall. They won’t treat an active infection, but they may help as one piece of a prevention strategy.