Can you tell me exactly when is a sun burn bad enough to go to the doctor?

It's bad enough when: See this online mayo clinic article: http://www.Mayoclinic.Com/health/sunburn/ds00964/dsection=complications. Seek medical care for severe pain, fever, lack of improvement of symptoms within several days or if a large surface area is blistered. Open blisters are more likely to become infected - red, hot with pus- get seen. In meantime, aloe vera is helpful.