In medicine, it refers to things the patient feels or notices. It contrasts with signs, which are changes which a doctor sees in a patient. What a patient feels is subjective, whereas what a doctor sees is objective.
In diagnosis, all symptoms and signs are brought together to make a hypothesis as to what is going wrong. This might suggest further investigation or treatment. A complete investigation ends with a diagnosis that summarizes all this.
- Pain is a symptom, and red color a sign, of a skin burn.
- Feeling sick is a symptom, and vomiting and diarrhea are signs, of food poisoning, cholera and other causes.
- Pain in the chest is a symptom, and cyanosis (blue color of skin) is a sign, of heart disease.
- Headaches, aching muscles and nausea are symptoms of influenza.