Even a mysterious rash does not require a trip to your healthcare provider. However, you should always see a doctor if your rash worsens, lasts longer than a week, shows signs of infection, like redness, oozing, or swelling of the skin occurs together with chills, fever, swollen glands, or other infections, such as a cough, sore throat, nasal congestion, or headache. Another sign to see the doctor is when symptoms might point to an autoimmune disorder, like recurring fever, fatigue, weight loss, and joint swelling. The outlook for most rashes is promising, especially after the cause has been accurately identified.