Arthritis has name recognition, even among people who are not suffering from it. But despite that recognition, arthritis is not as well understood as one might think.

According to the Arthritis Foundation, arthritis is not a single disease, but rather an informal way of referring to joint pain or joint disease. In fact, the term “arthritis” is so wide-ranging that it actually refers to more than 100 types of conditions.

Despite that complexity, arthritis often produces four important warning signs, regardless of which type of arthritis a person may have.

1. Pain

The Arthritis Foundation notes that arthritis-related pain may be constant or intermittent. One common misconception about arthritis pain is that it only occurs during or shortly after a body is at rest. However, arthritis-related pain can occur while the body is at rest and is not always triggered by an activity that incorporates a part of the body affected by arthritis. In addition, pain from arthritis can be isolated to one area of the body or affect various parts of the body.

2. Swelling

Skin over the joints affected by arthritis may become red and swollen. This skin also may feel warm to the touch. The Arthritis Foundation advises anyone who experiences this swelling for three days or longer or more than three times per month to contact a physician.

3. Stiffness

This warning sign is, along with pain, the one that is most often associated with arthritis, even by people who don’t suffer from the condition. Stiffness when waking up in the morning or after long periods of being sedentary, such as sitting at a desk during the workday or taking a long car ride, can be symptomatic of arthritis, especially if the stiffness lasts an hour or longer.

4. Difficulty moving a joint

The Arthritis Foundation notes that people should not experience difficulty moving, such as when getting out of bed. People who experience such difficulty may have arthritis.

People who recognize any of these warning signs should report them to their physicians immediately. Be as specific as possible when describing these symptoms, as specificity can help physicians design the most effective course of treatment.