Somatic symptom disorder is a mental illness that causes distressing physical symptoms without a clear medical cause. Treatment focuses on improving daily functioning rather than just symptoms, and may include therapy, stress reduction, and addressing any underlying mental health conditions. Hypochondriasis involves a persistent fear of having a serious illness despite reassurance. Illness anxiety disorder involves excessive worry about personal health without clear physical symptoms. These somatic symptom disorders can be chronic and difficult to treat, often requiring therapy and management of anxiety.