A Note About Disease, Illnesses, and Conditions: The Words Used to Describe Our Health

Difference between risk factors and etiology

Etiology is the study of causes of disease or injury. When someone refers to the etiology of a disease, they mean the cause of the disease. Etiology can include pathogens (as in infectious diseases) or physiological parameters like high blood pressure.

Risk factors are something else. Risk factors are items or states that appear in conjunction with the disease, whether or not there is a cause and effect relationship. Being a kid is a risk factor for measles, but childhood doesn’t cause measles - a virus does. Being a smoker is a risk factor for lung cancer; being old is also a risk factor for lung cancer. Being old is a bigger risk factor than being a smoker. Smoking causes lung cancer; old age does not cause cancer.

Being a woman is a risk factor for osteoporosis - women are more likely to get it than men. Being of East Asian ancestry is also a risk factor for osteoporosis. An East Asian ancestry doesn’t cause osteoporosis per se. We don’t know exactly the molecular causes of osteoporosis. We do know that being past the age of menopause is a risk factor.

To be a cause, the factor must happen before the disease shows up. Causes can be positive or negative, in which case the factor does not exist and its absence causes the malady.

Genetics plays the biggest role in determining the risk of osteoporosis, but diet, exercise, and illness can also play factors.


A symptom is some observable condition or state - observable to the patient or to an outsider with no technology. A sign is similar but one found through medical diagnostic techniques. The patient may not feel any symptoms even if he or she has signs of a disease.

A syndrome is a cluster of symptoms which are suspected to be related but which is not understood. A disorder is a cluster of symptoms that occur together often enough that medical professionals notice and give it a name. As with a syndrome, the etiology is unknown. There’s a fine line between a syndrome and a disorder. When the word syndrome is used, there is the implication that there is a unified cause, even if it is not understood. “Disorder” implies no conception of a connection between symptoms.

Prodrome is similar to sign and symptom and not used consistently. It is a sign or symptom that heralds or predicts disease onset well in advance. Predisease is also used. This has been adopted in the medical profession - or at least some drug companies - as a sign that intervention is called for to forestall development of a serious disease.

A disease disrupts the normal organ function and/or physiological processes. A formal definition of a particular disease lists changes in performance of one or more organs and probably histological or other laboratory results from analysis of the body. The description usually includes causes and/or risk factors and typical prognosis. Traditionally there are four kinds of disease – hereditary, pathogenic, physiological and deficiency.

Illness is subjective. It is what a person feels. If a person feels unwell, he or she has an illness.

Diseases often cause illness, although that is not always the case. Heart disease often has no symptoms.

Sick means a person is ill and others recognize the illness. A person living alone on a desert island could get ill but could not get sick. Medical research papers never use the word sick.

Public health thinker Eric Cassell wrote in the late 1970’s: "Disease... is something an organ has, illness is something a man has."

Osteoporosis and osteomalacia are considered diseases as is osteonecrosis. Osteopenia is not a disease; it’s a condition. Frailty syndrome is a syndrome. Hypogonadism is a sign and may point to a disease, but hypogonadism by itself is not considered a disease.

Drugs can be used to treat diseases but they are also used to address conditions and syndromes. Hypertension afflicts 80 million Americans and millions of prescriptions are taken to control it every year even though hypertension is not a disease itself. (It’s a condition that is a risk factor for several diseases.)


Infectious diseases occur when pathogens get inside the body. Osteoporosis is not a communicable disease. Although we do not know the exact causes of osteoporosis and other bone diseases, there is no evidence that they are communicable or infectious. (Communicable diseases can spread from one organism to another. Contagious diseases can spread from one human being to another. Zoonotic diseases spread from animals to humans.)

Medical researchers now suspect that many diseases long considered to be not infectious may indeed be caused by unknown pathogens. This is a minority view but some think heart disease may be partially caused by a virus or other germ. Prions, which were discovered only in the 1980s, may be the cause of Alzheimer's and other brain diseases long thought to have no external cause. This is all unknown at this time, but it is intriguing.

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