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Capitalizing COVID-19, Diabetes, and Down Syndrome Correctly

Published on June 16, 2025 by Marvin Erdner

Diseases, theories, and objects are sometimes named after their discoverers. But do we capitalize the resulting compounds?

Correct Spelling
  • The majority of diseases are spelled in lowercase, unless they are at the beginning of a sentence.
      • ○ The doctor suggested he should eat healthy because diabetes runs in his family.
      ○ Obesity is associated with the leading cause of death, according to the CDC (Center for Disease Control and Prevention).
  • Disease names that are acronyms are spelled with capital (uppercase) letters: AIDS, SARS, COVID-19, etc.
  • The first letter of theories, units, methods, inventions, or concepts that are named after a person should be capitalized: Murphy’s law, Ponzi scheme, Geiger counter, etc.
  • However, if a one-word unit is named after a real person, you spell it in lowercase: volt, watt, hertz, etc.

Capitalization of Proper Nouns

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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Marvin Erdner

Writing is simply in his blood! After finishing high school, Marvin first traveled to South America before studying English and Spanish linguistics in Augsburg. After graduating, this native of northern Germany returned to the north—this time not to Hanover, but to Hamburg. When he's not questioning German spelling rules, he's probably on Netflix, using Babbel, or traveling abroad. But his greatest passion is writing. Was that mentioned already?