Joint pain has dozens of possible causes, ranging from everyday wear and tear to infections that need urgent treatment. About 67 million U.S. adults have some form of diagnosed arthritis, and osteoarthritis alone accounts for nearly half of those cases. But arthritis is only one piece of the picture. Injuries, infections, autoimmune conditions, and even body weight all play a role.
Osteoarthritis: The Most Common Cause
Osteoarthritis is behind roughly 50% of all arthritis diagnoses in the U.S., affecting an estimated 33 million adults. It happens when the cartilage cushioning the ends of your bones gradually breaks down. Inflammatory proteins in the joint trigger enzymes that chew through cartilage’s two main structural components: collagen (the fiber that gives cartilage its strength) and proteoglycans (the molecules that help it absorb shock). Over time, the cartilage thins and roughens, leaving bone surfaces exposed to friction.
The risk climbs steeply with age. Only about 3% of adults aged 20 to 44 have osteoarthritis, but that figure jumps to around 11% by ages 45 to 54, 23% by ages 55 to 64, and over 34% for those 75 and older. Knees, hips, hands, and the spine are the joints most often affected. The pain typically worsens with activity and improves with rest, at least in early stages. Stiffness after sitting or sleeping is common but usually loosens within 30 minutes or so.
Rheumatoid Arthritis and Autoimmune Causes
Unlike osteoarthritis, rheumatoid arthritis (RA) is driven by the immune system attacking the lining of the joints. About 10.6 million U.S. adults have it. RA typically shows up as symmetrical joint swelling, meaning both wrists or both knees at the same time, and morning stiffness that can last an hour or more. Small joints in the hands and feet are often the first to be affected.
Doctors look at four factors to identify RA: how many joints are swollen, whether blood tests show specific antibodies, whether markers of inflammation are elevated, and how long symptoms have lasted. A score of 6 or higher out of 10 across those domains points to a diagnosis. RA prevalence rises with age, from about 2% of adults in their 20s and 30s to roughly 7.5% of those 75 and older.
Other autoimmune conditions that cause joint pain include psoriatic arthritis (linked to the skin condition psoriasis, affecting about 1 million U.S. adults), lupus, and ankylosing spondylitis, which primarily targets the spine and pelvis.
Gout and Other Metabolic Causes
Gout produces some of the most intense joint pain you can experience. It strikes when uric acid in the blood exceeds about 6.8 mg/dL, the concentration at which needle-shaped crystals start forming and depositing in joints. The big toe is the classic target, but gout can hit ankles, knees, wrists, and fingers too.
A gout flare often starts suddenly, frequently in the middle of the night. The joint becomes hot, swollen, and so tender that even the weight of a bedsheet can feel unbearable. Flares typically peak within 12 to 24 hours and can last days to weeks. Between flares, you may feel completely normal. Over time, frequent flares can cause lasting joint damage if uric acid levels aren’t managed.
Pseudogout is a related condition where calcium crystals, rather than uric acid, accumulate in joints. It tends to affect the knees and wrists and is more common in older adults.
Infections That Cause Joint Pain
Joint pain sometimes signals an infection that needs prompt attention. Septic arthritis occurs when bacteria enter a joint directly, often after surgery, an injury, or through the bloodstream. It causes rapid-onset, severe pain in a single joint, usually with swelling, warmth, and fever. Delayed treatment can lead to permanent joint damage, so sudden, intense pain in one joint with fever warrants immediate medical evaluation.
Viral infections are a far more common trigger of temporary joint aches. Chikungunya, dengue, hepatitis B and C, parvovirus, Epstein-Barr virus, and COVID-19 can all cause joint pain that typically resolves as the infection clears, though chikungunya in particular can cause joint symptoms lasting months.
Lyme disease is another infectious cause worth knowing about. It accounts for roughly one in four reported Lyme cases. Lyme arthritis usually develops one to several months after a tick bite. The hallmark is obvious swelling of one or a few large joints, most often the knee. The swelling can come and go or migrate between joints.
Bursitis and Tendinitis
Not all “joint pain” actually originates in the joint itself. Bursitis and tendinitis involve the soft tissues surrounding a joint and are easy to mistake for a joint problem. Bursae are small fluid-filled sacs that cushion the space between bones, muscles, and tendons. Tendons are the thick cords connecting muscle to bone. When either becomes inflamed, the result is localized pain and stiffness that worsens with movement.
Shoulders, elbows, hips, and knees are the most common sites for both conditions. Repetitive motions, prolonged pressure (like kneeling), and sudden increases in physical activity are typical triggers. The pain often intensifies at night. Most cases improve with rest and reduced activity over a few weeks, though recurrence is common if the underlying movement pattern doesn’t change.
Fibromyalgia and Widespread Pain
Fibromyalgia can feel like your joints ache everywhere, but it’s actually a disorder of pain processing in the nervous system rather than inflammation or damage in the joints themselves. To meet current diagnostic criteria, pain must be present in at least four of five body regions (left side, right side, above the waist, below the waist, and the spine) and persist for at least three months.
Diagnosis uses two scales: a widespread pain index that maps 19 body areas where you’ve had pain in the past week, and a symptom severity score that accounts for fatigue, unrefreshing sleep, and cognitive difficulties (often called “fibro fog”). The combination of these scores determines whether fibromyalgia is the likely explanation. Because standard blood tests and imaging come back normal, fibromyalgia is often diagnosed only after other causes have been ruled out.
How Body Weight Affects Your Joints
Extra body weight doesn’t just add a little stress to your joints. It multiplies it. Walking on flat ground puts a force equal to 1.5 times your body weight on each knee. Going up or down stairs increases that to two to three times your body weight. That means even 10 extra pounds translates to 30 to 50 additional pounds of force on your knees with every step on a staircase.
Beyond the mechanical load, excess body fat produces inflammatory compounds that circulate throughout the body. This helps explain why obesity increases the risk of osteoarthritis not only in weight-bearing joints like knees and hips, but also in hands, where excess load isn’t a factor. Weight loss, even modest amounts, can meaningfully reduce both pain and the rate of cartilage loss.
Injuries and Overuse
Sprains, dislocations, fractures, and torn ligaments or cartilage are obvious causes of joint pain. But injuries don’t always announce themselves dramatically. A partially torn meniscus in the knee or a labral tear in the hip can develop gradually from repetitive stress, producing a nagging ache that slowly worsens over weeks or months. Previous joint injuries also raise your long-term risk of osteoarthritis in that joint, sometimes by several decades.
When Joint Pain Needs Urgent Attention
Most joint pain develops gradually and responds to rest, activity modification, or over-the-counter anti-inflammatory options. But certain patterns signal something more serious. A single joint that becomes intensely painful, swollen, warm, and red within hours, especially with fever, could indicate septic arthritis or a gout flare. Septic arthritis in particular can cause irreversible joint destruction if not treated quickly. Joint pain following a tick bite in an area where Lyme disease is common also warrants evaluation, especially if you notice swelling in a large joint like the knee. And joint pain accompanied by unexplained weight loss, persistent fatigue, or rashes may point to an autoimmune condition that benefits from early treatment.