O doador de sangue deve se hidratar.

In Portuguese, o doador de sangue literally means the blood donor, but it can also be used in a generic sense, meaning a blood donor / blood donors in general.

So in this sentence, o doador de sangue deve se hidratar is not necessarily about one specific donor. It often means something like:

• A blood donor should hydrate.
• Blood donors should stay hydrated.

Portuguese often uses the singular with a definite article to talk about a whole category of people.

Word by word:

• o = the
• doador = donor
• de = of
• sangue = blood

So doador de sangue is literally donor of blood, which is the normal Portuguese way to say blood donor.

English often puts nouns together (blood donor), while Portuguese commonly connects them with de.

Portuguese usually links two nouns with de where English might use a noun as an adjective.

Compare:

• blood donor → doador de sangue
• wine bottle → garrafa de vinho
• school bus → ônibus escolar or sometimes a structure with de, depending on the phrase

So de sangue tells you what kind of donor this is: a donor of blood.

Deve is from the verb dever. In this sentence, it usually means should or ought to.

So:

• deve se hidratar = should hydrate / should stay hydrated

Depending on context, deve can also mean:

• must
• is supposed to
• sometimes even probably in other sentence types

But here, with a health recommendation, should is the best natural translation.

Se is there because hidratar-se is being used as a reflexive verb, meaning to hydrate oneself.

So:

• hidratar = to hydrate
• hidratar-se = to hydrate oneself / to become hydrated / to keep oneself hydrated

In English, we usually do not say hydrate oneself in everyday speech, but Portuguese uses this structure naturally.

So deve se hidratar literally means something like:

• should hydrate himself/herself
• more naturally: should stay hydrated

No. Hidratar can be used in different ways.

Examples:

• O creme hidrata a pele. = The cream hydrates the skin.
• Ela precisa se hidratar. = She needs to hydrate / stay hydrated.

So:

• hidratar can take a direct object
• hidratar-se is used when the subject is the one receiving the action

In your sentence, the donor is the one who needs hydration, so se hidratar makes sense.

Both are possible, but in Brazilian Portuguese, deve se hidratar is the more common and natural everyday order.

So in Brazil:

• deve se hidratar = very common
• deve hidratar-se = correct, but more formal or more typical of careful written style

This is about clitic placement (where little pronouns like me, te, se, o, a go). Brazilian Portuguese strongly prefers putting se before the infinitive in many everyday situations like this one.

Here se does not specifically tell you gender in translation. It matches the third person and can correspond to:

• himself
• herself
• themselves in some contexts
• or more naturally in English, no separate word at all

Since o doador de sangue is singular, se refers back to that person. But in natural English, you would usually just say:

• The blood donor should stay hydrated.

rather than should hydrate himself/herself.

Yes, o doador is grammatically masculine singular.

If you want to refer specifically to a female donor, you would say:

• A doadora de sangue deve se hidratar.

So:

• o doador = male donor / generic donor
• a doadora = female donor

In many contexts, the masculine singular can be used generically, but if you want to be explicitly inclusive or specific, you can change it.

No. Sangue does not need to agree with doador here.

In doador de sangue:

• doador is the main noun
• de sangue is a prepositional phrase describing it

Only articles, adjectives, and some other words agree with the noun they belong to. Since sangue is inside a de phrase, it just stays sangue.

So this is normal:

• o doador de sangue
• a doadora de sangue
• os doadores de sangue
• as doadoras de sangue

Notice that sangue stays the same each time.

Yes. Deve is present tense.

Portuguese often uses the present tense to express:

• general truths
• instructions
• recommendations
• rules

So O doador de sangue deve se hidratar is like saying:

• A blood donor should stay hydrated
• Blood donors should stay hydrated

It is a general recommendation, not necessarily something happening right now.

Yes, Brazilians do say se hidratar, especially in health-related advice. It sounds natural.

You might also hear:

• beber bastante água = drink plenty of water
• manter-se hidratado = stay hydrated
• tomar bastante líquido = drink plenty of fluids

So deve se hidratar is perfectly normal, but depending on context, a speaker might choose a more specific everyday phrase.

A careful approximate pronunciation is:

• O doador de sangue deve se hidratar
• oo doh-ah-DOR djee SANG-ghee DEH-vee see ee-drah-TAR

A few helpful notes:

• doador has stress on the last syllable: do-a-DOR
• sangue sounds roughly like SANG-ghee
• deve is DEH-vee
• hidratar ends with stress on -tar: ee-drah-TAR

In natural speech, sounds may run together a bit, but those stressed syllables are the most important ones to catch.