Achy joints have dozens of possible causes, ranging from normal wear and tear to infections, autoimmune conditions, and simple inactivity. The most common culprit is osteoarthritis, which affects roughly 528 million people worldwide. But joint pain can also flare up temporarily from a virus, show up after a long stretch on the couch, or signal something that needs medical attention.
Osteoarthritis: The Most Common Cause
Osteoarthritis happens when the cartilage cushioning the ends of your bones gradually breaks down. Without that smooth layer, bones start grinding against each other, causing pain, stiffness, and sometimes a creaking or popping sound called crepitus. It most often hits the knees, hips, hands, and spine.
About 73% of people living with osteoarthritis are older than 55, and 60% are female. But age alone doesn’t explain it. A joint injury earlier in life, repetitive stress from certain jobs or sports, and carrying extra weight all accelerate cartilage loss. The global number of osteoarthritis cases has jumped 113% since 1990, driven partly by aging populations and partly by rising obesity rates.
Weight plays a surprisingly large role. When you walk on flat ground, your knees absorb a force equal to about one and a half times your body weight. Climb stairs, and that jumps to two to three times your weight. Squat down to pick something up, and each knee handles four to five times your body weight. Even a modest amount of extra weight compounds quickly under those multipliers.
Autoimmune and Inflammatory Conditions
Not all joint pain comes from physical wear. In autoimmune conditions, the immune system mistakenly attacks healthy joint tissue, causing inflammation, swelling, and pain that can feel very different from osteoarthritis.
Rheumatoid arthritis is the most well-known example. It usually develops between the ages of 30 and 60 and tends to affect the same joints on both sides of the body, like both wrists or both knees at once. Lupus is another autoimmune disease that frequently causes joint and muscle pain alongside symptoms in other organs. Sjögren’s syndrome, best known for causing dry eyes and dry mouth, also commonly triggers joint aches.
The key difference between inflammatory and wear-and-tear joint pain is how it behaves. Inflammatory arthritis typically causes morning stiffness lasting an hour or more after you wake up. Osteoarthritis stiffness, by contrast, tends to ease once you start moving. Inflammatory conditions also tend to affect multiple joints at once and produce more constant pain, while osteoarthritis usually starts in one joint and comes and goes.
Viral Infections and Temporary Joint Pain
If your joints started aching alongside a fever, sore throat, or general feeling of being unwell, a viral infection is a likely explanation. Many common viruses trigger joint pain as part of the body’s inflammatory response to fighting off the infection.
The list of viruses that can cause this is longer than most people expect. It includes COVID-19, hepatitis B and C, parvovirus (sometimes called “fifth disease”), Epstein-Barr virus, chikungunya, dengue, Zika, mumps, rubella, and even some herpes viruses. The joint pain typically develops quickly, over hours or days, and resolves on its own once the infection clears. For most viruses, that means days to a few weeks. It doesn’t cause long-term joint damage.
Overuse Injuries: Bursitis and Tendinitis
Repetitive motion can inflame the structures around a joint even when the joint itself is fine. Two of the most common overuse injuries are bursitis and tendinitis.
Bursae are small fluid-filled sacs that cushion the space between bones, muscles, and tendons. When a bursa gets irritated from repetitive movement, it swells with extra fluid and makes the joint painful. This is especially common in the shoulders, elbows, hips, and knees. Tendinitis works similarly: a tendon becomes inflamed from overuse, making the joint it crosses painful to move. Both conditions improve with rest, but they tend to come back if the repetitive activity continues without modification.
How Inactivity Makes Joints Ache
It sounds counterintuitive, but too little movement can cause just as much joint pain as too much. Cartilage doesn’t have its own blood supply. It relies on the compression and release of normal movement to draw in nutrients from synovial fluid, the slippery liquid inside your joints. When you sit for long stretches, that nutrient exchange slows down, and cartilage can start to deteriorate.
Animal research has confirmed this directly. When weight-bearing on the hind limbs of mice was reduced, both the total amount and thickness of cartilage dropped significantly. Physical activity, on the other hand, enhances synovial fluid metabolism and may even benefit the bone just beneath the cartilage surface. This is one reason why low-impact movement like walking, swimming, or cycling is consistently recommended for joint health, even for people who already have arthritis.
How to Tell What Type of Joint Pain You Have
A few patterns can help you narrow down the cause before you see a provider:
- One joint vs. many. Pain in a single joint, especially a weight-bearing one like the knee or hip, points toward osteoarthritis or an overuse injury. Multiple joints aching at the same time suggests an inflammatory or autoimmune condition.
- Morning stiffness. Stiffness that lasts less than 30 minutes and improves with movement is typical of osteoarthritis. Stiffness lasting an hour or more is a hallmark of inflammatory arthritis.
- Grinding or popping. Crepitus, that creaky, grinding sensation when you bend a joint, is strongly associated with osteoarthritis and worn cartilage.
- Timing. Pain that came on suddenly alongside flu-like symptoms is more likely viral. Pain that’s been building gradually over months or years is more likely degenerative.
Symptoms That Need Prompt Attention
Most achy joints don’t require urgent care, but a few combinations of symptoms do. Joint pain accompanied by redness, swelling, warmth around the joint, and fever could indicate an infection inside the joint itself, which is a medical emergency. If an injury caused your joint pain and the joint looks misshapen, you can’t use it at all, the pain is severe, or there’s sudden swelling, that also warrants immediate evaluation.
What Helps Achy Joints
The right approach depends on the cause, but several strategies help across the board. Staying physically active is one of the most effective things you can do. Regular low-impact exercise strengthens the muscles supporting your joints, improves cartilage nutrition, and reduces stiffness. If excess weight is a factor, even a small reduction meaningfully lowers the force your joints absorb with every step.
For osteoarthritis specifically, glucosamine supplements have shown promise as a safe option for reducing knee pain, with studies evaluating both short-term (under three months) and long-term benefits. Results vary from person to person, but it’s one of the more evidence-supported supplements available for joint discomfort.
For inflammatory and autoimmune conditions, treatment focuses on calming the immune response. These conditions generally require a diagnosis and a tailored plan, since the underlying mechanism is fundamentally different from wear-and-tear arthritis. The earlier inflammatory arthritis is identified, the more effectively joint damage can be slowed or prevented.