Many people use the words 'sign' and 'symptom' interchangeably. However, there are important differences that affect their use in the field of medicine.

Any objective evidence of a disease, such as a skin rash or a cough, is a sign. A doctor, family members, and the individual experiencing the signs can identify these.

However, less obvious breaks in normal function, such as stomachache, lower back pain, and fatigue, are symptoms and can only be recognized by the person experiencing them. Symptoms are subjective, meaning that other people only know about them if informed by the individual with the condition.

This MNT Knowledge Center article will look at the implications of signs and symptoms as well as their history. The piece will also introduce the different types of sign and symptom and their uses in medicine.

Fast facts on signs and symptoms

  • A light headache can only ever be a symptom because no one else can observe it.
  • Medical symptoms are split into chronic, relapsing, and remitting.
  • An example of a medical sign is high blood pressure, as it can be measured and observed by another person.
  • Anthony van Leuwenhoek invented the microscope in 1674, forever changing the face of diagnostic tools.

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A sign is the effect of a health problem that can be observed by someone else. A symptom is an effect noticed and experienced only by the person who has the condition.

The key difference between signs and symptoms is who observes the effect.

For example, a rash could be a sign, a symptom, or both:

  • If the patient notices the rash, it is a symptom.
  • If the doctor, nurse, or anyone other than the patient notices the rash, it is a sign.
  • If both the patient and doctor notice the rash, it can be classed as both a sign and a symptom.

Regardless of who notices that a system or body part is not functioning normally, signs and symptoms are the body's ways of letting a person know that not everything is running smoothly. Some signs and symptoms need follow-up by a medical professional, while others may completely resolve without treatment.

The diagnosis of symptoms and signs has come a long way since Hippocrates needed to taste the urine of a patient

The identification of signs has become increasingly more dependent on the doctor as time and technology have progressed.

When Antony van Leeuwenhoek invented the microscope and used it to discover cells and microbes in 1674, he opened up the possibility of identifying signs of disease completely invisible to the naked eye. These include foreign organisms in the blood and urine, changes in the composition of blood and waste material, and other important, microscopic signs.

These indicators can be the difference between normal function and dangerous diseases and conditions.

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Advancing technology has put more power in the hands of clinicians when it comes to identifying diseases.

Since the 1800s, medical science has come on leaps and bounds in helping physicians clearly identify signs. A range of devices is now available to help doctors identify and analyze signs that even the patient may not have recognized.

These include:

  • Stethoscope: A doctor can use this to listen to the sounds of the heart and lungs.
  • Spirometer: This helps to measure lung function.
  • Ophthalmoscope: An eye specialist may use this to examine the inside of the eye.
  • X-ray imaging: This can show damage to the bones.
  • Sphygmomanometer: This is a device that fits around the arm and measures blood pressure.

During the 20th century, hundreds of new devices and techniques were created to evaluate signs. It was during this period in modern medical history that the terms "sign" and "symptom" developed separate meanings, as doctors and patients no longer needed to work together as closely to identify medical issues.

Doctors can now see signs they would previously have relied upon patients to describe. By the modern definition, these would have been symptoms but are now classed as signs.

There are three main types of symptom:

  • Remitting symptoms: When symptoms improve or resolve completely, they are known as remitting symptoms. For examples, symptoms of the common cold may occur for several days and then resolve without treatment.
  • Chronic symptoms: These are long-lasting or recurrent symptoms. Chronic symptoms are often seen in ongoing conditions, such as diabetes, asthma, and cancer.
  • Relapsing symptoms: These are symptoms that have occurred in the past, resolved, and then returned. For instance, symptoms of depression may not occur for years at a time but can then return.

Some conditions show no symptoms at all. For example, a person can have high blood pressure for years without knowing, and some cancers have no symptoms until the later, more aggressive stages. These are known as asymptomatic conditions, and even though the idea of symptoms is often linked to discomfort or abnormal function, a condition without symptoms can be deadly.

Many types of infection do not show symptoms. These are known as subclinical infections, and they can be contagious despite not causing noticeable symptoms in the person carrying the infection. The infection can still be transmitted to other people during the incubation period, or the period during which the infectious agent takes hold of the body.

Another danger of subclinical infections is that they can cause complications unrelated to the infection itself. For example, untreated urinary tract infections (UTIs) may cause premature births.

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Many infections, such as HPV, do not immediately show symptoms and can still be transmitted to others.

Examples of infections that do not cause symptoms initially are HIV, human papillomavirus (HPV) herpes simplex virus (HSV), syphilis, and hepatitis B and C.

The first time a person will be aware of many asymptomatic conditions is during a visit to a doctor, normally concerning a different problem. It is important to undergo regular health checks to identify any underlying problems that may not be obvious.

Many cancers are asymptomatic during their early stages. Prostate cancer, for example, does not show symptoms until it has advanced to a certain point. This is what makes some cancers so dangerous, as early treatment is often crucial when treating cancer.

For this reason, regular screening tests are important for at-risk individuals.

A medical sign is a physical response linked medical fact or characteristic that is detected by a physician, nurse, or medical device during the examination of a patient. They can often be measured, and this measurement can be central to diagnosing a medical problem.

Sometimes, a patient may not notice a sign, and it may not seem relevant. However, in the hands of a medical professional that knows how this sign relates to the rest of the body, the same sign can be the key to treating an underlying medical problem.

Some examples of signs that can be linked to a disease by a clinician:

  • High blood pressure: This can indicate a cardiovascular problem, an adverse reaction to medication, an allergy, or many other possible conditions or diseases. This will often be combined with other signs to reach a diagnosis.
  • Clubbing of the fingers: This may be a sign of lung disease or a range of genetic diseases.

Doctors are trained to pick up signs that an untrained individual might not see as important.

Signs fit into the following categories:

  • Prognostic signs: These are signs that point to the future. Rather than indicating the nature of the disease, they predict the outcome for the patient, such as what is likely to happen to them and how severe the disease will probably be.
  • Anamnestic signs: These signs point to parts of a person's medical history. For instance, skin scars may be evidence of severe acne in the past.
  • Diagnostic signs: These signs help the doctor recognize and identify a current health problem. For example, high levels of prostate-specific antigen (PSA) in the blood of a male may be a sign of prostate cancer or a prostate problem.
  • Pathognomonic signs: This means that a doctor can link a sign to a condition with full certainty. For example, the presence of a certain microbe in a blood sample can point to a specific viral infection.

While there are differences between signs and symptoms, they are both ultimately methods the body uses to communicate health problems and trigger the search for a solution.

It is important not to ignore symptoms you discover by yourself or any signs found by a doctor.