Names are capitalized, common nouns are not; that is one of the basic rules of English spelling. This distinction gets fuzzy when a compound noun consists of a proper name. We show you when you need to use lowercase, and when it’s necessary to capitalize labels for sicknesses, hypotheses, units of measurement, etc.
Capitalization of Diseases
The majority of diseases are spelled in lowercase, as their etymology shows borrowings from Greek or Latin:
E.g., arthritis, asthma, autism, cancer, chlamydia, diabetes, epilepsy, flu, influenza, herpes, gonorrhea, hepatitis, meningitis, obesity, stroke, trichomoniasis, mononucleosis, kidney disease, chronic fatigue syndrome, lung cancer, traumatic brain injury, multiple sclerosis.
Some names—especially for viruses or bacteria—are actual acronyms, meaning they represent the capitals of a multi-word unit. These labels are spelled only with capital (uppercase) letters:
COVID-19 (aka coronavirus disease), HIV (aka human immunodeficiency virus), AIDS (aka acquired immunodeficiency syndrome), ADHD (aka attention deficit hyperactivity disorder), MERS (aka Middle East respiratory syndrome), SARS (aka severe acute respiratory syndrome), etc.
An exception to these conventions are illnesses that are named after their discoverer, or that are related to a geographic place.
Asperger syndrome (or Asperger’s), Alzheimer’s, Down syndrome, Crohn's disease, Parkinson’s, Norwalk virus, Lyme syndrome, Huntington’s disease, Ebola virus (named after the Ebola river in Congo), Zika virus (named after the Ziika Forest in Uganda).
Tip: Look out for apostrophes!
Capitalization of Theories and Units
The same principle applies for theories, units, methods, inventions, or concepts that are named after a person: The first letter of the name should be capitalized.
Pavlovian conditioning, Pythagoras’ theorem (also: theorem of Pythagoras), Murphy’s law, Ponzi scheme, Geiger counter, Richter magnitude scale (also: Richter scale or Richter’s magnitude scale), Heimlich maneuver, Freudian slip, degree Celsius, degree Fahrenheit, etc.
However, this rule applies only if the noun consists of more than one word. If a one-word unit is named after a real person, you spell it in lowercase.
E.g., hertz, roentgen, tesla, sievert, gray, becquerel, newton, volt, watt.
LanguageTool reminds you to use a capital letter whenever you type a compound noun with a proper name in it. Besides this spelling check, the writing tool also corrects your grammar errors and style mistakes. After learning many theories and formulas, it helps you avoid agonizing over spelling rules. No headache should stand between you and a flawless text.
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