Hyphenation is the part of Brazilian spelling that even educated native speakers double-check in a dictionary. The 1990 reform (the AO90) rebuilt the whole system around a single organizing idea: look at the junction — the last letter of the prefix and the first letter of the base it attaches to. Almost every decision falls out of comparing those two letters. This page gives you the working rules for prefixed words and for the separate world of compound nouns. Because the principles are mechanical, once you internalize the junction logic you can hyphenate words you have never seen.
The core principle: it is all about the junction
When you attach a prefix (anti-, super-, micro-, contra-, auto-, ...) to a base word, ask what the end of the prefix and the start of the base are. Three outcomes are possible: hyphen, simple join, or join-with-doubling. English barely uses hyphens with prefixes anymore ("antiinflammatory" → "anti-inflammatory" is one of the few survivors), so this whole apparatus has no real English parallel; you have to build the habit from scratch.
Rule 1 — Same vowel at the junction → hyphen
If the prefix ends in a vowel and the base begins with the same vowel, use a hyphen. Doubling vowels inside a single word would be hard to read, so the hyphen keeps them apart.
| Prefix | Base | Result | Meaning |
|---|---|---|---|
| micro- (o) | onda (o) | micro-ondas | microwave |
| anti- (i) | inflamatório (i) | anti-inflamatório | anti-inflammatory |
| contra- (a) | ataque (a) | contra-ataque | counterattack |
| auto- (o) | observação (o) | auto-observação | self-observation |
✅ Esquenta trinta segundos no micro-ondas e está pronto.
Heat it thirty seconds in the microwave and it's ready.
✅ O médico receitou um anti-inflamatório para o joelho.
The doctor prescribed an anti-inflammatory for the knee.
Rule 2 — Different vowel, or a consonant → join (no hyphen)
If the prefix ends in a vowel but the base begins with a different vowel, or with most consonants, the two simply join into one word with no hyphen. This is the AO90's big simplification — many words that used to take hyphens now run together.
| Prefix | Base | Result | Meaning |
|---|---|---|---|
| auto- (o) | escola (e) | autoescola | driving school |
| aero- (o) | espacial (e) | aeroespacial | aerospace |
| anti- (i) | aéreo (a) | antiaéreo | anti-aircraft |
| super- (r) | interessante (i) | superinteressante | super interesting |
| extra- (a) | oficial (o) | extraoficial | unofficial |
✅ Tirei a carteira de motorista numa autoescola perto de casa.
I got my driver's license at a driving school near home.
✅ Achei o documentário superinteressante, assisti duas vezes.
I found the documentary super interesting, I watched it twice.
Rule 3 — Prefix ends in vowel + base starts with r or s → double the r/s and join
When a prefix ending in a vowel meets a base beginning with r or s, you do not hyphenate. Instead you join the words and double the r or s, so the sound stays /ʁ/ (strong r) or /s/ rather than softening to a flap or /z/ between vowels. This is one of the most distinctive AO90 outcomes.
| Prefix | Base | Result | Meaning |
|---|---|---|---|
| anti- | racismo | antirracismo | anti-racism |
| ultra- | som | ultrassom | ultrasound |
| contra- | senha | contrassenha | countersign |
| auto- | retrato | autorretrato | self-portrait |
| micro- | sistema | microssistema | microsystem |
✅ A campanha de antirracismo ganhou força nas escolas.
The anti-racism campaign gained traction in schools.
✅ O exame de ultrassom confirmou que está tudo bem.
The ultrasound exam confirmed everything is fine.
Rule 4 — Base starts with h → hyphen
If the base word begins with h, keep a hyphen so the h stays visible and is not swallowed. This holds regardless of what the prefix ends in.
| Prefix | Base | Result | Meaning |
|---|---|---|---|
| anti- | higiênico | anti-higiênico | unhygienic |
| super- | homem | super-homem | superman |
| pré- | história | pré-história | prehistory |
| sobre- | humano | sobre-humano | superhuman |
✅ Deixar a louça suja a noite toda é meio anti-higiênico.
Leaving dirty dishes out all night is kind of unhygienic.
✅ Ele agiu com uma força sobre-humana para salvar o cachorro.
He acted with superhuman strength to save the dog.
Rule 5 — Prefix ends in the same consonant the base starts with → hyphen
When the last letter of the prefix equals the first letter of the base (and it is a consonant), use a hyphen to keep the doubled consonant readable. This commonly happens with super-, inter-, hiper- before r, and with prefixes ending in a vowel/consonant that match.
| Prefix | Base | Result | Meaning |
|---|---|---|---|
| super- (r) | resistente (r) | super-resistente | super resistant |
| inter- (r) | racial (r) | inter-racial | interracial |
| hiper- (r) | realista (r) | hiper-realista | hyper-realistic |
| sub- (b) | base (b) | sub-base | sub-base |
✅ Comprei uma capa super-resistente para o celular.
I bought a super-resistant case for the phone.
✅ O Brasil é um país inter-racial por natureza.
Brazil is an interracial country by nature.
The special case of co-
The prefix co- is famously messy. The AO90 rule is that co- generally joins the base even before o and h, contrary to what the same-vowel and h rules would predict: coautor (co-author), coordenar (to coordinate), coabitar (to cohabit), coerdeiro (co-heir). Treat co- as a learned exception that prefers to fuse.
✅ Ela é coautora do livro e cuidou da revisão final.
She is the co-author of the book and handled the final revision.
Compound nouns keep their hyphens
Hyphenated compound nouns — words built from two independent words, often without a prefix — are a separate category and the reform left most of them alone. They keep their hyphens.
| Compound | Built from | Meaning |
|---|---|---|
| guarda-chuva | guarda + chuva | umbrella ("guards rain") |
| guarda-roupa | guarda + roupa | wardrobe |
| beija-flor | beija + flor | hummingbird ("kisses flower") |
| segunda-feira | segunda + feira | Monday |
| couve-flor | couve + flor | cauliflower |
✅ Esqueci o guarda-chuva no ônibus e cheguei encharcado.
I left my umbrella on the bus and arrived soaked.
✅ Tem um beija-flor que visita a janela toda manhã.
There's a hummingbird that visits the window every morning.
A subtle point the AO90 did change: when elements lost their sense of being separate words, some compounds were written solid — paraquedas (parachute) and mandachuva (big shot) lost their hyphens, while guarda-chuva kept its. There is no perfect rule for which compounds fused; this is genuine dictionary territory. See nouns/compound-nouns for how these pluralize.
bem- and mal-
The adverbs bem- and mal- form their own little system. Bem- usually keeps a hyphen (bem-vindo, bem-estar, bem-humorado). Mal- takes a hyphen only before a vowel or h (mal-humorado, mal-estar) and joins before a consonant (malcriado, malsucedido, malfeito).
✅ Seja bem-vindo! Espero que esteja tudo bem com você.
Welcome! I hope everything is well with you.
✅ Ele acordou mal-humorado e ninguém conseguiu animá-lo.
He woke up in a bad mood and nobody could cheer him up.
✅ Foi um plano malsucedido desde o começo.
It was an unsuccessful plan from the start.
Common Mistakes
❌ Comprei uma autoescola... digo, fui à auto-escola.
Incorrect — auto- + escola have different junction vowels, so they join: autoescola.
✅ Fui à autoescola fazer a prova prática.
I went to the driving school for the practical test.
❌ O médico pediu um ultra-som.
Incorrect — prefix ending in vowel + s doubles and joins: ultrassom.
✅ O médico pediu um ultrassom.
The doctor ordered an ultrasound.
❌ A luta antirracista virou um movimento anti racismo.
Incorrect — anti- + racismo doubles the r and joins: antirracismo.
✅ A luta antirracista virou um movimento antirracismo.
The anti-racist struggle became an anti-racism movement.
❌ Ele é um superhomem nos quadrinhos.
Incorrect — a base starting with h takes a hyphen: super-homem.
✅ Ele é um super-homem nos quadrinhos.
He is a superman in the comics.
❌ Acordou bem humorado e mau-criado ao mesmo tempo.
Incorrect — bem-humorado keeps its hyphen; mal- joins before a consonant: malcriado.
✅ Acordou bem-humorado, mas o filho estava malcriado.
He woke up in a good mood, but his son was being rude.
Key takeaways
- Same vowel at the junction → hyphen (micro-ondas, anti-inflamatório).
- Different vowel / most consonants → join (autoescola, antiaéreo).
- Prefix ends in vowel + r/s base → join and double (antirracismo, ultrassom).
- Base starts with h → hyphen (super-homem, anti-higiênico).
- Same consonant at the junction → hyphen (super-resistente, inter-racial).
- co- prefers to fuse (coautor); compound nouns keep their hyphens (guarda-chuva); bem- hyphenates, mal- hyphenates only before a vowel/h.
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Start learning Portuguese→Related Topics
- Common PrefixesB1 — The productive Brazilian Portuguese prefixes — negation, repetition, intensity, and position — most of which map directly onto English, plus the post-AO90 hyphenation rules.
- Acordo Ortográfico (AO90) in BRB1 — The spelling reform that reshaped Brazilian Portuguese — out went the trema, the acute on paroxytone ei/oi, the circumflex on double-o and -eem, and disambiguating accents; in came k/w/y and new hyphen rules.
- Compound NounsB1 — How Brazilian Portuguese builds compound nouns from noun+noun, verb+noun, and prepositional patterns — and the unpredictable rules for pluralizing each type.
- BR Spelling: OverviewA1 — A map of the Brazilian Portuguese writing system: the 26-letter alphabet, the five diacritics and what each one does, sound-to-spelling regularity, the 2009 Acordo Ortográfico, and the main trouble spots.
- Accent Mark RulesA2 — The rules for when to write an accent in Brazilian Portuguese: all proparoxytones, oxytones ending in -a/-e/-o/-em, paroxytones ending the 'unusual' way, the hiatus rule, and the accents removed by the 2009 reform.