Kidney damage results from a surprisingly wide range of causes, from chronic conditions like diabetes and high blood pressure to everyday medications, infections, and even environmental exposures. About 1 in 7 U.S. adults, roughly 35.5 million people, already have some degree of chronic kidney disease, and as many as 9 in 10 of them don’t know it. Understanding what harms your kidneys is the first step toward protecting them.
Diabetes and High Blood Pressure
These two conditions are responsible for the majority of chronic kidney disease cases, and they often work together. Uncontrolled blood sugar damages the kidneys through several overlapping pathways. High glucose levels increase oxidative stress inside kidney cells and cause the tiny blood-filtering units (called glomeruli) to work under abnormally high pressure. Over time, this triggers inflammation and scarring that progressively destroys functional kidney tissue.
Healthy kidneys have a built-in pressure regulation system: small blood vessels automatically tighten or relax to keep the filtering pressure steady regardless of what your overall blood pressure is doing. In people with diabetes, this protective mechanism breaks down. When that happens, high blood pressure gets transmitted directly into the delicate filtering structures, accelerating damage. The combination of metabolic injury from high blood sugar and physical injury from uncontrolled pressure makes diabetic kidney disease particularly aggressive.
Common Pain Medications
Over-the-counter painkillers are one of the most overlooked causes of kidney damage. Nonsteroidal anti-inflammatory drugs, commonly known as NSAIDs, reduce blood flow to the kidneys by constricting the small vessels that supply them. Occasional use in a healthy person is generally fine, but regular or heavy use can cause both sudden and gradual kidney injury.
The NSAIDs most commonly associated with kidney harm include ibuprofen (sold as Advil and Motrin), naproxen (Aleve), and aspirin when used for pain relief. Prescription-strength versions carry the same risk. For people who already have reduced kidney function, even short courses of these drugs can be unsafe. If you rely on NSAIDs frequently for chronic pain, that’s worth a conversation with your doctor about alternatives.
Sudden Kidney Injury
Not all kidney damage develops slowly. Acute kidney injury, or AKI, is a rapid decline in kidney function that can happen over hours or days. The most common cause in people outside the hospital is simply reduced blood flow to the kidneys, which can result from severe dehydration, heavy blood loss, or a major drop in blood pressure. In hospitalized patients, the leading cause is direct damage to the kidney’s filtering tubes, accounting for about 45% of cases.
Sepsis, a life-threatening response to infection, is the single most common trigger of severe AKI in critically ill patients. The inflammatory cascade from sepsis damages kidney tissue through a combination of reduced blood flow, direct cellular injury, and swelling. Contrast dye used during CT scans and certain imaging procedures is another well-known cause. The dye can constrict blood vessels in the kidney and directly damage the filtering tubes, which is why medical teams monitor kidney function closely before and after contrast-based imaging.
Physical Blockages
When urine can’t drain properly, pressure builds up behind the obstruction and damages the kidney from within. Kidney stones are one of the most common culprits, but enlarged prostate tissue in older men is another frequent cause. Tumors of the prostate, bladder, cervix, or rectum can also compress the urinary tract and block flow. Even a blood clot in the ureter or a condition called retroperitoneal fibrosis, where scar tissue forms behind the abdominal organs, can create a blockage.
Obstruction-related damage is often reversible if caught early. But if the blockage persists, the sustained pressure causes permanent scarring and loss of function in the affected kidney.
Kidney Infections
A urinary tract infection that climbs from the bladder up to the kidneys causes pyelonephritis, a serious infection of the kidney tissue itself. Even when antibiotics successfully clear the bacteria, the body’s own inflammatory response can leave lasting damage. The intense inflammation triggered by the infection leads to scarring and fibrosis of functional kidney tissue.
Severe pyelonephritis is the primary cause of acquired kidney scarring in children. In a small but significant number of patients, these scars contribute to high blood pressure and progressive chronic kidney disease that may not become apparent until years later. Recurrent kidney infections compound the risk, with each episode potentially adding more scar tissue.
Autoimmune and Genetic Conditions
Your immune system can turn against your kidneys. Lupus nephritis, a complication of systemic lupus erythematosus, occurs when immune-driven inflammation attacks the kidney’s filtering structures. Signs include protein or blood in the urine and rising blood pressure. Diagnosis typically requires urine and blood tests, and sometimes a kidney biopsy to assess how much damage has occurred.
On the genetic side, polycystic kidney disease causes fluid-filled cysts to grow throughout the kidneys, gradually replacing healthy tissue and impairing function. Other forms of glomerulonephritis, where the immune system inflames the kidney’s filters, can arise from various autoimmune conditions or even follow certain infections. These conditions account for a smaller share of kidney disease overall but tend to affect younger patients who may not suspect kidney problems.
Heavy Metal Exposure
Long-term exposure to certain heavy metals damages the kidney’s tubular cells, the structures responsible for reabsorbing useful substances and excreting waste. Lead accumulates in these cells over years or even decades, initially causing subtle dysfunction like impaired uric acid handling (which can lead to gout) before progressing to permanent scarring and kidney failure. Chronic lead exposure over 5 to 30 years or more can cause progressive tubular atrophy and irreversible loss of function.
Cadmium, found in cigarette smoke, certain industrial settings, and contaminated food, causes similar tubular damage. Early signs include abnormal amounts of small proteins spilling into the urine. Mercury and gold compounds also target the kidneys, though they tend to damage the filtering units more than the tubes. Occupational exposure is the biggest risk factor, but environmental contamination from industrial waste can also contribute.
High Protein Diets
Whether high protein intake harms kidneys is one of the more nuanced questions in nutrition. In people with healthy kidneys, current evidence shows limited danger from high-protein diets. However, in people who already have reduced kidney function, even mild, the picture changes significantly. The Nurses’ Health Study, which followed women for 11 years, found that every 10-gram increase in daily protein intake was associated with a measurable decline in kidney filtration rate among women with mild kidney impairment. This association was not seen in women with normal kidney function.
The mechanism is straightforward: high protein intake forces the kidneys to filter more aggressively, increasing pressure inside the glomeruli. In healthy kidneys, this extra workload is manageable. In kidneys that are already compromised, it accelerates the loss of function. This is why protein restriction is a standard dietary recommendation for people with diagnosed kidney disease, while it’s generally unnecessary for those with healthy kidneys.
How Kidney Damage Is Measured
Kidney function is tracked using a number called the estimated glomerular filtration rate, or eGFR, which measures how efficiently your kidneys filter blood. A normal eGFR is 90 or above. The stages of chronic kidney disease break down as follows:
- Stage 1 (eGFR 90+): Normal filtration rate, but other signs of kidney damage are present, such as protein in the urine.
- Stage 2 (eGFR 60-89): Mildly decreased function.
- Stage 3a (eGFR 45-59): Mild to moderate decrease.
- Stage 3b (eGFR 30-44): Moderate to severe decrease.
- Stage 4 (eGFR 15-29): Severe decrease in function.
- Stage 5 (eGFR below 15): Kidney failure.
The tricky part is that kidneys can lose a substantial amount of function before you notice any symptoms. Stages 1 through 3 often produce no obvious warning signs, which is why routine blood and urine tests are the only reliable way to catch damage early. The CDC estimates that 9 out of 10 adults with chronic kidney disease are unaware they have it. A simple blood test that includes eGFR, paired with a urine test checking for protein, can reveal kidney damage years before symptoms appear.