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In medicine, a sign is something that can be detected or measured, in contrast to a symptom, which is generally a subjective experience of disease. For example, a sign might be something such as blood in the stool, a skin rash that can be recognised by a doctor, or a high body temperature. A symptom, on the other hand, can only be experienced (or sensed) and reported by the patient, such as stomach ache, lower-back pain, and fatigue. Sometimes, a sign may not be noticed by the patient, but is meaningful and helpful for the doctor for diagnosis. For example:

A rash – this could be a sign, symptom, or both:

  • If the patient notices the rash it is a symptom.
  • If the doctor, nurse or anyone else (but not the patient) notices the rash it is a sign.
  • If both the patient and doctor notice the rash it is both a sign and a symptom.

A light headache – this can only be a symptom:

  • A light headache can only be a symptom because it is only ever detected by the patient.
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