A joint flare is a period when psoriatic arthritis symptoms suddenly worsen — more pain, more swelling, more stiffness than the usual baseline. Stress, an infection, or cutting back on treatment too quickly can all bring one on. Recognising a flare promptly is often the trigger to reach out to a care team.

Joint erosion is the slow wearing away of bone at the edges of a joint, caused by inflammation that's gone unchecked for a while. Left untreated, it can eventually lead to joint deformity or loss of function. This is a major reason doctors favour starting treatment early rather than waiting.