Symptoms are the manifestations of the disease related by a patient to a physician.  These tend to be subjective, such as headache, nausea and pain and cannot be measured directly.  Many different diseases can be associated with the same set of symptoms.

Signs are clinical manifestations of disease that are visible, including vomiting, diarrhea, coughing and sneezing, fever, petechiae (reddish streaks or marks on the skin or mucus membranes), changes in normal pigmentation such as jaundice and lesions.

The combination of signs and symptoms is called the disease syndrome.

Some diseases may go undetected since no signs or symptoms are visible.  Asymptomatic diseases, such as Trichmonas vaginalis in males and occasionally Salmonella typhi can go undetected, though they can be spread to others. Subclinical infections by viruses such as measles and bacteria such as S. pyogenes may persist for many years and the infected individual may become an unintentional carrier of the disease.