Blood in your urine can come from anywhere along your urinary tract, from your kidneys down to your urethra. The most common causes are urinary tract infections, kidney stones, and an enlarged prostate in men. Less often, it signals something more serious like bladder or kidney cancer. Sometimes what looks like bloody urine turns out to be harmless discoloration from foods or medications.
Visible blood (pink, red, or cola-colored urine) and invisible blood (detected only on a urine test) can have different implications, so the cause matters more than the appearance alone.
Urinary Tract Infections
Infections are one of the most frequent reasons people notice blood in their urine. Bacteria irritate and inflame the lining of the bladder or urethra, which can cause small amounts of bleeding. You’ll typically also have burning during urination, a frequent urge to go, and cloudy or strong-smelling urine. Kidney infections can cause blood in the urine along with back or flank pain, fever, and chills. A simple urine test confirms the infection, and antibiotics usually clear it within a few days.
Kidney Stones
Kidney stones form when minerals in your urine crystallize into hard deposits. These stones start deep in the kidney tissue and gradually grow until they break through into the space where urine collects. As a stone moves through the ureter (the narrow tube connecting your kidney to your bladder), it scrapes and irritates the lining, causing bleeding. About 85% of people with kidney stones have at least some blood in their urine.
The pain is often the more noticeable symptom. Stones cause intense, cramping pain in your side, back, or lower abdomen as the ureter stretches and spasms around the stone. Some small stones pass on their own with just fluids and pain management, while larger ones may need medical procedures to break them up or remove them.
Enlarged Prostate
In men, the prostate gland surrounds the urethra just below the bladder. As men age, the prostate commonly enlarges, a condition called benign prostatic hyperplasia (BPH). This growth brings extra blood vessels with it, and those vessels can bleed into the urinary tract. BPH is one of the most common causes of blood in the urine for men over 50, alongside urinary infections and cancer. Other signs include a weak urine stream, difficulty starting urination, and needing to urinate frequently at night.
Kidney Disease
Your kidneys filter blood through tiny structures called glomeruli, which act like microscopic sieves. When these filters become inflamed or damaged, red blood cells leak through into your urine. This type of bleeding often produces cola-colored or tea-colored urine rather than bright red, and it frequently shows up alongside protein in the urine and sometimes foamy urine or swelling in the legs and feet.
Several conditions can damage these filters, including IgA nephropathy (the most common form of kidney inflammation worldwide), lupus-related kidney disease, and infections that trigger an immune response against the kidneys. Polycystic kidney disease, where fluid-filled cysts grow in the kidneys, is another cause. Some of these conditions are inherited, like thin basement membrane disease, which runs in families and is generally harmless despite causing persistent microscopic blood in the urine.
Bladder and Kidney Cancer
Painless visible blood in your urine is the hallmark warning sign of bladder cancer. This is why doctors take blood in the urine seriously even when nothing else seems wrong. Among people who can see blood in their urine, about 17% are eventually diagnosed with bladder cancer, and about 2% with kidney cancer. When blood is only found on a lab test (not visible), the cancer risk drops significantly: roughly 3.3% for bladder cancer and under 1% for kidney cancer.
Risk factors that increase concern include being over 50, smoking history, exposure to industrial chemicals, and a history of radiation to the pelvis. Bladder cancer is more common in men, but women who develop it tend to be diagnosed at a later stage. Prostate cancer can also cause blood in the urine, though this is less common than with bladder cancer.
Exercise-Related Bleeding
Intense physical activity, particularly long-distance running, cycling, and swimming, can cause blood to appear in your urine temporarily. The exact mechanism varies: repeated impact can irritate the bladder wall, and intense exertion may reduce blood flow to the kidneys temporarily, causing minor damage.
For most people, exercise-induced blood in the urine clears within about two days. A study of athletes found 81% had clear urine within three days, and 12% took up to a week. If blood in your urine lasts longer than two weeks after exercise, it’s unlikely to be from the workout alone. Three individuals in that study whose blood persisted beyond 14 days all turned out to have underlying kidney disease.
Foods and Medications That Mimic Blood
Not everything that turns your urine red is actually blood. Beets, blackberries, and rhubarb can all give urine a reddish or pinkish tint. Certain medications produce similar discoloration. Mesalazine, used for inflammatory bowel disease, creates a red-brown pigment when its metabolites are excreted. Some laxatives and antibiotics do the same.
This is called pseudohematuria: red urine without any actual red blood cells present. A simple urine test at your doctor’s office can tell the difference in minutes. If you recently ate beets and noticed red urine with no pain or other symptoms, that’s the most likely explanation, but confirming it with a test is straightforward.
Other Causes
Blood-thinning medications don’t cause blood in the urine on their own, but they can make bleeding from an existing problem more noticeable. Sickle cell disease damages small blood vessels in the kidneys, leading to bleeding. Direct trauma to the kidneys or bladder from an injury, fall, or car accident can cause sudden, sometimes heavy blood in the urine. In women, endometriosis can occasionally involve the urinary tract and cause cyclical blood in the urine around menstruation.
Signs That Need Urgent Attention
Most causes of blood in the urine aren’t emergencies, but certain combinations of symptoms are. Blood clots in your urine that make it difficult or impossible to urinate require immediate care, because clots can block the flow of urine entirely. Visible blood paired with dizziness, rapid heart rate, or feeling faint suggests significant blood loss.
Fever with blood in the urine and back pain can indicate a kidney infection spreading into the bloodstream. Severe, uncontrollable pain alongside bloody urine points to a possible obstructing kidney stone that may need intervention. Blood in the urine after any trauma to your abdomen, back, or pelvis also warrants prompt evaluation to rule out organ damage.
Painless blood in your urine, even just once, still deserves a medical evaluation. It may turn out to be something benign, but the absence of pain doesn’t rule out serious causes like cancer, and catching those early makes a significant difference in outcomes.