Osteoarthritis and rheumatoid arthritis are the 2 most common types of arthritis.
Osteoarthritis is the most common type of arthritis in the UK, affecting nearly 9 million people.
It most often develops in adults who are in their mid-40s or older.
It's also more common in women and people with a family history of the condition.
But it can occur at any age as a result of an injury or be associated with other joint-related conditions, such as gout or rheumatoid arthritis.
Osteoarthritis initially affects the smooth cartilage lining of the joint. This makes movement more difficult than usual, leading to pain and stiffness.
Once the cartilage lining starts to roughen and thin out, the tendons and ligaments have to work harder.
This can cause swelling and the formation of bony spurs called osteophytes.
Severe loss of cartilage can lead to bone rubbing on bone, altering the shape of the joint and forcing the bones out of their normal position.
The most commonly affected joints are those in the:
In the UK, rheumatoid arthritis affects more than 400,000 people.
It often starts when a person is between 40 and 50 years old. Women are 3 times more likely to be affected than men.
In rheumatoid arthritis, the body's immune system targets affected joints, which leads to pain and swelling.
The outer covering (synovium) of the joint is the first place affected.
This can then spread across the joint, leading to further swelling and a change in the joint's shape. This may cause the bone and cartilage to break down.
People with rheumatoid arthritis can also develop problems with other tissues and organs in their body.
The symptoms of arthritis you experience will vary depending on the type you have.
This is why it's important to have an accurate diagnosis if you have:
Arthritis is often associated with older people, but it can also affect children.
In the UK, about 15,000 children and young people are affected by arthritis.
Most types of childhood arthritis are known as juvenile idiopathic arthritis (JIA).
JIA causes pain and inflammation in 1 or more joints for at least 6 weeks.
Although the exact cause of JIA is unknown, the symptoms often improve as a child gets older, meaning they can lead a normal life.
The main types of JIA are:
Oligo-articular JIA is the most common type of JIA. It affects up to 4 joints in the body, most commonly in the knees, ankles and wrists.
Oligo-articular JIA often goes away without causing long-term joint damage.
But there's a risk that children with the condition may develop eye problems, so regular eye tests with an eye care specialist called an ophthalmologist are recommended.
Polyarticular JIA, or polyarthritis, is the second most common type of JIA and affects 5 or more joints.
It can affect a child of any age and may come on suddenly or develop gradually.
The symptoms of polyarticular JIA are similar to the symptoms of adult rheumatoid arthritis.
A child with the condition may also feel unwell and may occasionally have a high temperature of 38C or above.
Systemic onset JIA begins with symptoms such as a fever, rash, a lack of energy and enlarged glands. Later on, joints can become swollen and inflamed.
Like polyarticular JIA, systemic onset JIA can affect children of any age.
Enthesitis-related arthritis is a type of juvenile arthritis that often affects the joints of the leg and spine, causing inflammation where the tendons attach to the bone.
It can cause stiffness in the neck and lower back in the teenage years.
It's also linked to a painful eye condition called acute uveitis.
Versus Arthritis has more information about the different types of juvenile idiopathic arthritis.
There's no cure for arthritis, but there are many treatments that can help slow it down.
For osteoarthritis, treatments include lifestyle changes, medications and surgery.
Treatment for rheumatoid arthritis aims to slow the condition's progress and minimise joint inflammation. This helps prevent joint damage.
Treatments include medication, physiotherapy and surgery.
Versus Arthritis provides help and support for people in the UK with arthritis, plus their families and friends.
They have a free helpline you can call for further information and support on 0800 5200 520, Monday to Friday, 9am to 8pm.
You can also look up arthritis services near where you live.
Our guide to care and support explains your options and where you can get support.