Arthritis is inflammation in one or more joints that causes pain, swelling, and stiffness. It’s not a single disease but a broad category covering more than 100 conditions, and it affects roughly 1 in 5 American adults. Some forms wear down cartilage over years of use, while others involve the immune system attacking healthy joint tissue. Understanding which type you’re dealing with matters because the causes, progression, and management differ significantly.
How Arthritis Works Inside the Joint
Healthy joints are cushioned by cartilage, a smooth, rubbery tissue that lets bones glide against each other without friction. A thin membrane called the synovium lines the joint capsule and produces fluid that keeps everything lubricated. Arthritis disrupts this system in different ways depending on the type, but the end result is similar: inflammation, pain, and gradual loss of function.
In osteoarthritis, cartilage slowly breaks down from years of mechanical stress. As that cushion thins, bones begin rubbing closer together, causing pain, stiffness, and sometimes bony growths called bone spurs. In rheumatoid arthritis, the immune system mistakenly attacks the synovial membrane, causing it to thicken and swell. Over time, this inflamed tissue can invade and destroy cartilage, bone, tendons, and ligaments within the joint.
The Most Common Types
Osteoarthritis
Osteoarthritis is the most common form. It develops when cartilage wears away over time, and it tends to affect weight-bearing joints like the knees, hips, and spine, along with the hands. Symptoms usually come on gradually: stiffness after sitting or sleeping, aching during or after activity, and eventually reduced range of motion. It’s often called “wear and tear” arthritis, though inflammation plays a bigger role than that nickname suggests.
Rheumatoid Arthritis
Rheumatoid arthritis is an autoimmune disease where the body’s immune system attacks the joints, starting with their lining. It typically shows up as symmetric joint pain, meaning both hands, both wrists, or both feet are affected at the same time. Beyond the joints, it can involve the skin, heart, lungs, and eyes. Because it’s driven by immune activity rather than mechanical wear, it can strike at any age and tends to cause more widespread fatigue and malaise than osteoarthritis.
Gout
Gout develops when uric acid crystals build up in a joint, triggering intense, sudden episodes of pain and swelling. The base of the big toe is the classic location, though it can affect ankles, knees, and wrists. Attacks often come on overnight and peak within 12 to 24 hours. Men are more likely to develop gout than women.
Psoriatic Arthritis
Psoriatic arthritis occurs in some people who have the skin condition psoriasis. Joint pain, stiffness, and swelling can affect any joint, and it sometimes causes fingers and toes to swell into a puffy, sausage-like shape. It can also cause pain where tendons attach to bone, particularly in the feet, and may lead to eye inflammation that causes redness, pain, and blurry vision.
Ankylosing Spondylitis
This form primarily targets the spine and pelvis, causing pain and stiffness that tends to be worse in the morning or after periods of inactivity. Over time, it can fuse vertebrae together, limiting flexibility. It often begins in early adulthood and tends to run in families.
Arthritis in Children
Arthritis isn’t limited to older adults. Juvenile idiopathic arthritis affects children under 16 and is diagnosed when a child has unexplained joint pain, stiffness, or swelling lasting at least six weeks. One serious complication is eye inflammation, which can develop silently and lead to vision problems like glaucoma or cataracts if not caught early. Children who test positive for certain antibodies are at higher risk for this eye involvement and need more frequent screening with an eye doctor.
Risk Factors You Can and Can’t Control
Some risk factors are built in. Women are more likely to develop osteoarthritis, rheumatoid arthritis, and fibromyalgia, while men are more prone to gout. Risk increases with age, partly because joints accumulate damage over time and muscle mass decreases, leaving joints less stable. Family history plays a role too, particularly for rheumatoid arthritis, lupus, and ankylosing spondylitis.
Other risk factors are modifiable. Carrying extra weight puts significant stress on knees and hips, making knee osteoarthritis both more likely and more painful. Smoking increases the risk of developing rheumatoid arthritis and makes existing arthritis harder to manage. Joint injuries, whether from sports, falls, or repetitive work tasks, raise the odds of osteoarthritis in that joint later in life. Jobs that require frequent bending, squatting, or repetitive motions also increase risk. Military veterans have higher rates of arthritis, likely tied to injuries sustained during service.
Certain infections can trigger joint inflammation as well. Lyme disease, staph infections, and gonorrhea are examples of infections that can cause joints to swell, turn red, and feel warm, potentially setting the stage for longer-term problems.
How Arthritis Is Diagnosed
There’s no single test that confirms all types of arthritis, so diagnosis usually involves a combination of physical examination, blood work, and imaging. For rheumatoid arthritis, blood tests measure markers of inflammation in the body, including something called sed rate and C-reactive protein. Additional tests look for specific antibodies: rheumatoid factor and anti-CCP antibodies. These help distinguish rheumatoid arthritis from other types.
Imaging fills in the rest of the picture. X-rays can show joint damage and cartilage loss, and doctors use them to track how the disease progresses over time. MRI and ultrasound offer more detailed views and can detect early changes that X-rays miss. For osteoarthritis, diagnosis is often based primarily on symptoms, physical examination, and X-ray findings rather than blood work.
What Symptoms Feel Like Day to Day
The hallmark symptoms across most types of arthritis are joint pain, stiffness, and swelling. But the pattern varies. Osteoarthritis stiffness is usually worst first thing in the morning or after sitting for a while, and it tends to loosen up within 15 to 30 minutes. Rheumatoid arthritis stiffness often lasts longer, sometimes an hour or more, and comes with noticeable fatigue that goes beyond just being tired.
Gout is different from both. It hits suddenly, often waking you up at night with a joint that’s swollen, hot, and so tender that even the weight of a bedsheet feels unbearable. Between flares, you may feel completely fine. Psoriatic arthritis can fluctuate too, with periods of increased symptoms and periods of relative calm, and it may include skin symptoms like scaly patches alongside joint problems.
Exercise and Physical Activity
Exercise is one of the most effective tools for managing arthritis symptoms, even though moving a painful joint feels counterintuitive. The key is consistency over intensity. Low-impact activities like walking, swimming, water aerobics, cycling, and elliptical training are easier on joints while still building strength and improving flexibility.
A good target is 150 minutes of moderate aerobic exercise per week, broken into whatever chunks work for your joints. You should be breathing harder than usual but still able to hold a conversation. If you haven’t been active, start slowly. Doing too much too fast tends to increase pain rather than reduce it. Range-of-motion exercises, where you gently move each joint through its full arc of motion, can be done daily and help reduce stiffness. Strength training at least two days a week builds the muscle support that protects joints from further damage.
A few practical tips make a real difference. Warming up with gentle range-of-motion movements for 5 to 10 minutes before exercise prepares your joints. Applying heat beforehand, whether a warm towel, hot pack, or warm shower for about 20 minutes, relaxes muscles and eases pain. After exercise, icing sore joints for up to 20 minutes helps control any swelling that flares up.
How Common Arthritis Really Is
As of 2024, 21.3% of American adults have been diagnosed with some form of arthritis, according to the CDC. That’s roughly one in five adults, making it one of the leading causes of disability in the United States. The number rises sharply with age, but arthritis is not exclusively a condition of older people. Autoimmune forms like rheumatoid arthritis and ankylosing spondylitis frequently begin in young adulthood, and juvenile idiopathic arthritis affects thousands of children. The sheer prevalence means most people will either develop arthritis themselves or care for someone who has it.