In everyday language, people use the words 'signs' and 'symptoms' interchangeably when talking about a disease. However, in biology and medicine, there is a very strict and important difference between the two.
A disease that has no symptoms at all is called an Asymptomatic disease. High blood pressure (hypertension) is often called a 'silent killer' because it presents objective signs but rarely any subjective symptoms until it is severe.
A Symptom is a subjective experience. It is something that only the patient feels and can describe. A doctor cannot 'see' or measure a symptom directly; they have to rely on the patient telling them about it.
A Sign is an objective piece of evidence. It is something that the doctor can physically see, hear, feel, or measure during a medical examination, regardless of what the patient says.
| Feature | Symptom | Sign |
|---|---|---|
| Nature | Subjective (felt by patient) | Objective (observed by doctor) |
| Measurement | Cannot be easily measured | Can be verified and measured |
| Who reports it? | The patient | The physician / medical tests |
| Example | 'My throat hurts.' | Red, swollen tonsils. |
A cough is interesting because it can be **both**. It is a symptom when the patient complains 'I have been coughing all night', and it is a sign when the doctor physically hears the patient coughing in the clinic.
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