Using capitals in scientific writing: Rules, tips, examples

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• Why Capitalization Matters in Academic Writing
• Core Capitalization Rules
• Capitalization in Titles and Headings: Sentence Case vs Title Case
• Capitalization in the Life Sciences
• Capitalization in Medicine and Clinical Sciences
• Capitalization in the Physical Sciences
• Capitalization in the Social Sciences
• Capitalization in the Humanities
• The Trickiest Cases: A Quick-Reference Table
• Common Mistakes to Avoid
• Summary of Capitalization Rules Across Major Style Guides

 

Introduction

Capitalization is one of the most nuanced conventions in academic and scientific writing. Get it wrong and you signal unfamiliarity with your field; get it right and your manuscript looks polished, authoritative, and publication-ready. The difficulty is that capitalization rules in scientific writing are not uniform across disciplines, and even within a single field, style guides disagree. Capitalization is certainly a problem that confronts writers and editors, and the space devoted to capitalization by many style guides is one indication of how common the problem is: New Hart’s Rules¹, Scientific Style and Format², and AMA Manual of Style³ each devotes a whole chapter to it. This guide covers the core principles that apply across all sciences and humanities, then drills into the conventions specific to life sciences, medicine, physical sciences, social sciences, and the humanities. It also highlights the most common mistakes researchers make and how to fix them.  

Why Capitalization Matters in Academic Writing

Capitalization serves two functions in scientific prose:

• grammatical (marking the start of a sentence, signaling proper nouns) and
• semantic (distinguishing a specific named entity from a general concept).

Misuse in either direction creates confusion.

• Over-capitalization is the most common error. Writers capitalize words to signal importance: “the Study found,” “the Gene was expressed,” “Western Medicine.” None of these warrants a capital letter.
• Under-capitalization of true proper nouns like names, places, and established theories, makes writing look careless.
• Inconsistency within a single manuscript is perhaps the most damaging pattern, suggesting a lack of editorial control.

The baseline rule, shared by virtually every style guide (APA, AMA, Chicago, CSE, MLA), is this: Capitalize proper nouns and proper adjectives; use lowercase for common nouns and general concepts.  

Core Capitalization Rules

1. First Word of a Sentence

Every sentence begins with a capital letter. This rule seems self-evident, but two scientific writing situations complicate it.

• Lowercase-first terms at the start of a sentence. Some scientific terms are, by convention, always written with a lowercase first letter even at the start of a sentence. In these cases, the term retains its lowercase form, and you rewrite the sentence to avoid beginning with it, or accept the lowercase.

Term	Correct at sentence start
pH	pH values ranged from 6.2 to 7.4. (acceptable)
mRNA	mRNA was extracted using TRIzol reagent. (acceptable)
e-commerce	Rewrite: Online commerce has disrupted retail.

 

• Chemical names with italicized prefixes. Compounds such as cis-, trans-, ortho-, and tert– retain their italicized lowercase prefix at the start of a sentence, but the root word is capitalized normally.

• tert-Butanol was added to the mixture.
• cis-Platin was administered at a dose of 75 mg/m².

2. Proper Nouns and Proper Adjectives

A proper noun names a specific, unique entity: a person, place, institution, or formally designated thing. A proper adjective is derived from a proper noun.

Capitalize:

• Named individuals: Charles Darwin, Marie Curie, Sigmund Freud
• Geographic locations: the Amazon Basin, the Sahara Desert, the North Sea
• Institutions and organizations: the World Health Organization, the National Institutes of Health, Harvard Medical School
• Formally named theories, laws, and scales when bearing a person’s name: Newton’s Second Law of Motion, the Likert scale, the Richter scale, the Linnaean system

Do not capitalize:

• Generic references to the same concepts: the law of gravity, a rating scale, a classification system

3. Titles and Headings

In titles of papers, books, and journal articles, most style guides use either title case (all significant words capitalized) or sentence case (only first word + proper nouns capitalized).

Style guide	Approach	Example
APA (7th ed.)	Sentence case for article titles; title case for journal names	Cognitive flexibility and working memory in bilingual children. Psychological Science
Chicago	Title case for most titles	The Structure of Scientific Revolutions
AMA	Title case for book titles; sentence case for article titles	Harrison’s Principles of Internal Medicine
CSE	Sentence case for article titles	Effects of temperature on coral bleaching in the Great Barrier Reef

  In running headings within a paper (e.g., Introduction, Methods, Discussion), most scientific journals use title case for main section headers and sentence case for subheadings, but always defer to the target journal’s author guidelines.

4. After a Colon

Whether to capitalize the first word after a colon depends on what follows:

• Capitalize if an independent clause follows: This study addresses one central question: What drives antibiotic resistance in community settings?
• Do not capitalize if a list or dependent phrase follows: Three variables were measured: temperature, pressure, and humidity.
• Capitalize each clause when multiple independent clauses follow a colon: Two questions guided this inquiry: What causes neuronal apoptosis in early Alzheimer’s disease? How can this process be slowed?

 

Capitalization in Titles and Headings: Sentence Case vs Title Case

Two capitalization styles govern headings, titles, and subheadings in scientific writing: title case and sentence case.

What is Title Case?

In title case, capitalize the first letter of most words. The exceptions are:

• Articles: a, an, the (unless first or last word)
• Short prepositions: in, on, at, by, for, of, up, to (unless first or last word)
• Coordinating conjunctions: and, but, or, nor, so, yet
• The “to” in infinitives: How to Measure Cortisol Levels

Example: The Effects of Sleep Deprivation on Working Memory in Adolescents

What is Sentence Case?

In sentence case, capitalize only the first word of the title and any proper nouns or proper adjectives.

• Everything else remains lowercase, including words that feel important
• Proper nouns (gene names, place names, named scales) are still capitalized and so are abbreviations that typically capitalized (USA, WHO, DNA, etc.).
• The first word after a colon is also capitalized in some styles

Example: The effects of sleep deprivation on working memory in adolescents

Title case vs sentence case across major style guides

Context	Title case	Sentence case
APA journal article titles	✗	✓
APA journal names	✓	✗
Chicago book and article titles	✓	✗
CSE journal article titles	✗	✓
AMA book titles	✓	✗
AMA article titles	✗	✓
Most journal section headings	✓	✗
Most journal subheadings	✗	✓

  The safest habit: check the style guide specified in your target journal’s author guidelines and look at a recent published article in that journal to confirm.  

Capitalization in the Life Sciences

Life sciences (biology, ecology, genetics, microbiology, biochemistry) have some of the most specific capitalization conventions in all of academia.

Taxonomic Names

The binomial nomenclature system follows strict capitalization rules established by the International Code of Nomenclature:

• Genus names are always capitalized and italicized: Homo, Escherichia, Quercus
• Species epithets are always lowercase and italicized: Homo sapiens, Escherichia coli, Quercus robur
• Higher taxonomic ranks (family, order, class, phylum, kingdom) are capitalized when used as formal names, but lowercase when used descriptively

Formal name (capitalize)	Descriptive use (lowercase)
Mammalia	mammals
Rosaceae	the rose family
Proteobacteria	proteobacteria
Chordata	chordates

Abbreviated genus names (E. coli, H. sapiens) follow the same rules: capitalized abbreviation, lowercase species epithet, both italicized.

Genes and Proteins

Gene and protein nomenclature follows conventions set by bodies such as HUGO (for human genes) and MGI (for mouse genes). The rules differ by organism and between genes and their protein products.

Entity	Convention	Example
Human gene symbol	Italicized, all caps	BRCA1, TP53
Human protein	Roman (non-italic), all caps	BRCA1, TP53
Mouse gene symbol	Italicized, first letter cap only	Brca1, Trp53
Mouse protein	Roman, all caps	BRCA1, TRP53
Drosophila gene	Italicized, all lowercase or initial cap (by convention)	wingless (wg), Notch

Common error: Capitalizing a gene when referring to the protein, or italicizing the protein name.

• ✗ The patient had a mutation in BRCA1 protein.
• ✓ The patient had a mutation in the BRCA1 gene; the BRCA1 protein was absent.

Biological Terms

• Common names of organisms: lowercase (fruit fly, gray wolf, bread mold)
• Viruses: lowercase unless a proper noun is included (influenza virus, Ebola virus, SARS-CoV-2)
• Biological processes: lowercase (apoptosis, photosynthesis, meiosis)

 

Capitalization in Medicine and Clinical Sciences

Medical writing follows AMA (American Medical Association) style in most journals, with some journals adopting their own variations.

Diseases and Conditions

The AMA Manual of Style is clear: most disease names are lowercase, even when they feel important.

• ✗ The patient was diagnosed with Diabetes Mellitus Type 2.
• ✓ The patient was diagnosed with type 2 diabetes mellitus.

However, diseases named after people (eponyms) retain the proper noun but often drop the possessive apostrophe in modern AMA style:

Older form	Modern AMA style
Alzheimer’s disease	Alzheimer disease
Parkinson’s disease	Parkinson disease
Crohn’s disease	Crohn disease
Down’s syndrome	Down syndrome

Note: Some journals and style guides still use the possessive form. Always follow the target journal.

Capitalize:

• Formal diagnostic criteria names: Diagnostic and Statistical Manual of Mental Disorders (DSM-5)
• Named syndromes used as a proper noun in full form: Acquired Immune Deficiency Syndrome (but AIDS in subsequent references)

Drugs and Medications

• Generic drug names: always lowercase (metformin, ibuprofen, atorvastatin)
• Brand/proprietary names: always capitalized (Glucophage, Advil, Lipitor)
• Drug class names: lowercase (beta-blockers, ACE inhibitors, statins)

Anatomical Terms

Anatomical terminology follows Terminologia Anatomica. Most structures are lowercase in running text:

• the left ventricle, the hippocampus, the brachial plexus

Capitalize only when a proper name is embedded: the Circle of Willis, the Bundle of His, Broca’s area (but Broca area in modern style).  

Capitalization in the Physical Sciences

Physics, chemistry, astronomy, and earth sciences have their own distinct traditions.

Units and Measurements

This is a frequent source of error. The rule: the unit name is lowercase; the symbol is capitalized if derived from a proper name.

Unit	Symbol	Capitalized?
newton	N	Yes (named after Isaac Newton)
pascal	Pa	Yes (named after Blaise Pascal)
kelvin	K	Yes (named after Lord Kelvin)
meter	m	No
kilogram	kg	No
second	s	No

• ✗ The force was measured in Newtons.
• ✓ The force was measured in newtons (N).

Note: “Kelvin” (the scale) is capitalized; “kelvin” (the unit) is lowercase: The sample was cooled to 4 kelvin (4 K).

Chemical Names and Elements

• Element names: always lowercase in running text (hydrogen, carbon, uranium)
• Element symbols: always capitalized as given in the periodic table (H, C, U, Fe)
• Chemical compound names: lowercase (sulfuric acid, sodium chloride, ethanol) unless containing a proper noun (Fehling’s solution, Folin–Ciocalteu reagent)

Astronomical and Earth Science Terms

• Named celestial bodies: capitalize (Mars, the Milky Way, the Andromeda Galaxy, Pluto)
• Generic terms: lowercase (a galaxy, a planet, a nebula)
• Sun and Moon: capitalize when used as proper astronomical names (the Moon’s surface, solar output from the Sun); lowercase when used generically (the moon was full, she sat in the sun)
• Geological periods and epochs: capitalize formal names (the Cretaceous Period, the Pleistocene Epoch, the Jurassic)

 

Capitalization in the Social Sciences

Psychology, sociology, economics, political science, and anthropology largely follow APA (7th edition) style.

Psychological Constructs and Tests

• General psychological constructs: lowercase (working memory, self-efficacy, emotional regulation, executive function)
• Named psychological tests and scales: capitalize the full official name (Beck Depression Inventory, Minnesota Multiphasic Personality Inventory, the Stroop Color and Word Test)
• Shortened references: lowercase (the inventory, the scale, the test)

Theories and Models

• Named theories: capitalize the full name when using it as a formal designation (Cognitive Load Theory, Attachment Theory, Social Learning Theory)
• General descriptive references: lowercase (a cognitive load framework, attachment behaviors, social learning processes)

Example (APA style): Bandura’s Social Learning Theory proposes that behavior is acquired through observation. Social learning mechanisms have since been identified in non-human primates.

Groups, Identities, and Populations

APA 7th edition made important updates here: racial and ethnic group names are capitalized.

• ✓ Black, White, Indigenous, Latino, Asian American
• ✓ People with disabilities, autistic individuals, deaf community

Do not capitalize general descriptors used attributively: the urban population, low-income households, rural communities.

Research Terminology

• Conditions and groups in a study: lowercase in general use (the control group, the experimental condition, participants)
• Formal condition names in a specific study: can be capitalized for clarity (the Treatment Group, the Waitlist Control Condition). APA permits this when referring to a specific group in a specific study

 

Capitalization in the Humanities

History, literature, philosophy, linguistics, and cultural studies follow Chicago style (for most journals) or MLA for literature.

Historical Periods and Events

Capitalize formally recognized historical periods and named events:

Capitalize	Do not capitalize
the Renaissance	the rebirth of classical learning
the Industrial Revolution	the industrial period
the Cold War	postwar tension
the Great Depression	the economic downturn of the 1930s
the Enlightenment	enlightened political thought

Note: the Middle Ages is capitalized; medieval (the adjective derived from it) is lowercase.

Philosophical and Literary Terms

• Named philosophical movements and schools: capitalize (Existentialism, Kantian ethics, Stoicism, Marxism, Deconstructionism)
• Derived adjectives in common use: lowercase when they have shed their proper-noun identity (marxist critique, platonic relationship, stoic calm)
• Literary genres and forms: lowercase (tragedy, the novel, free verse, magical realism)
• Named literary works and their components: title case for titles; lowercase for generic references (Shakespeare’s tragedies, Homeric epics, the Romantic poets)

Languages, Nationalities, and Cultural Terms

• Languages and nationalities: always capitalize (English, Swahili, Japanese, French-Canadian)
• Academic disciplines: generally lowercase unless they contain a proper noun (history, philosophy, English literature, French linguistics)
• Religious texts and traditions: capitalize names of sacred texts and formal religious traditions (the Bible, the Quran, the Torah, Buddhism, Catholicism); lowercase general references (a religious text, monotheistic faith)

 

The Trickiest Cases: A Quick-Reference Table

Situation	Capitalize?	Example
Named law with person’s name	Yes	Newton’s Third Law
Generic “law” or “theory”	No	the law of conservation of mass
Disease eponym (AMA style)	Partial	Parkinson disease (no possessive)
Generic disease name	No	type 2 diabetes, hypertension
Gene symbol	Per organism convention	BRCA1 (human), Brca1 (mouse)
Protein product	Roman caps	BRCA1 protein
SI unit named after person	Lowercase word, capped symbol	newtons (N), pascals (Pa)
Taxonomic genus	Yes, italicized	Homo, Mus, Streptococcus
Taxonomic species	No, italicized	sapiens, musculus, pneumoniae
Historical period	Yes	the Renaissance, the Jurassic
Racial/ethnic group (APA)	Yes	Black, Indigenous, Latino
Study group in your paper	Optional (be consistent)	the Treatment Group
Generic drug	No	metformin, ibuprofen
Brand-name drug	Yes	Glucophage, Tylenol
Celestial body (formal)	Yes	the Moon, Mars, the Milky Way
Generic celestial reference	No	a planet, the moon rose

 

Common Mistakes to Avoid

• Over-capitalizing for emphasis. Capitalizing the Study, the Results, or the Authors in an abstract does not add authority but instead it signals unfamiliarity with conventions.
• Capitalizing job titles in running text. Write the professor conducted the study not the Professor conducted the study; capitalize only when the title immediately precedes a name: Professor Jane Doe conducted the study.
• Assuming eponyms always take possessives. Modern AMA and many medical journals have dropped the possessive from disease eponyms (Crohn disease, not Crohn’s disease). Check your target journal.
• Capitalizing abbreviations’ spelled-out forms. DNA is an acronym and is capitalized; deoxyribonucleic acid is lowercase.
• Inconsistent treatment of named theories. Decide whether you will capitalize theory names throughout a manuscript, and apply the choice consistently.

 

Summary of Capitalization Rules Across Major Style Guides

Style guide	Primary discipline	Title case for article titles	Eponym possessives	Gene symbols
APA 7th ed.	Social/behavioral sciences	No (sentence case)	Retained	Per organism
AMA Manual	Medicine/clinical	Yes (books); No (articles)	Dropped	Per HGNC/MGI
Chicago 17th ed.	Humanities/history	Yes	Author’s choice	N/A
CSE (Council of Science Editors)	Biological/life sciences	No (sentence case)	Retained or dropped	Per organism
ACS Style Guide	Chemistry	Yes	Author’s choice	N/A

Frequently Asked Question

Should I capitalize “Table,” “Figure,” and “Equation” when referring to them in the text?

Yes — when you refer to a specific labeled element in your manuscript by its number, capitalize it. These references function as proper designations for a unique item, not generic nouns.

• The results are shown in Table 3.
• See Figure 2 for the reaction pathway.
• As described in Equation 1…
• The results are shown in the table below.

The same rule applies to supplementary materials: Supplementary Table S1, Supplementary Figure 3. When referring to the element generically  without a number, you should use lowercase: each table was formatted identically, the figure captions were revised.

Should I capitalize the first word of each item in a bulleted or numbered list?

It depends on whether each item is a complete sentence. The standard convention:

• Full sentences in a list: capitalize the first word and end with a period.
• Fragments or short phrases: capitalize the first word; terminal punctuation is optional and often omitted.
• Items that complete a stem sentence: some style guides use lowercase to signal the grammatical continuation; others capitalize regardless. Choose one approach and apply it consistently throughout the document.

The key is consistency. Mixed capitalization within a single list (some items starting with capitals, others not) is always wrong regardless of which convention you follow.

How should I handle capitalization in hyphenated compounds in titles?

This is one of the most contested areas in title-case formatting. The general guidance across major style guides:

• Capitalize both elements if both are major words: Long-Term Effects, High-Resolution Imaging, Cross-Cultural Analysis
• Lowercase the second element if it is a minor modifier or article: Follow-up Study, State-of-the-art Methods
• Capitalize the second element if it is a proper noun or proper adjective regardless of position: Non-Newtonian Fluids, Post-Keynesian Economics
• In sentence case, only the first element is capitalized unless the second is a proper noun: Long-term effects of sleep deprivation, Non-Newtonian fluid dynamics

When in doubt, Chicago style recommends capitalizing both elements of a hyphenated compound in a title unless the second is an article, preposition, or coordinating conjunction.

How should I capitalize conditions, interventions, and timepoints that I defined in my own study, such as “baseline,” “week 12,” or “the intervention group”?

This is a matter of consistency and clarity rather than strict grammatical rule. APA style offers the clearest guidance: you may capitalize the names of specific conditions, groups, or timepoints in your study when doing so helps distinguish them from generic references. But you must apply the capitalization uniformly throughout the manuscript.

• ✓ Participants were assessed at Baseline, Week 6, and Week 12.
• ✓ The Intervention Group received daily supplementation; the Control Group received a placebo.
• ✗ The intervention group showed improvement at week 6, while the Intervention Group maintained gains at Week 12. (inconsistent)

The practical test: if a reader could confuse your specific study timepoint or group with a generic concept, capitalize to disambiguate. If the meaning is clear without it, lowercase is equally acceptable, as long as you are consistent.  

References:

[1] OUP. 2014. New Hart’s Rules: the Oxford style guide, 2nd edn. Oxford: Oxford University Press. 464 pp. [2] CSE , Style Manual Committee. 2014. Scientific Style and Format: the CSE manual for authors, editors, and publishers, 8th edn. Wheat Ridge, Colorado, USA: Council of Science Editors. 722 pp. [3] AMA. 2007. AMA Manual of Style: a guide for authors and editors, 10th edn. New York: Oxford University Press [and American Medical Association]. 1010 pp. This article was originally published on July 201, 2015, and updated on April 15, 2026.