La inyección duele.

Because inyección is a feminine noun in Spanish, so it takes the feminine singular article la.

• la inyección = the injection
• inyección ends in -ción, and nouns ending in -ción are very often feminine

So the article has to match the noun’s gender: la inyección.

Duele means hurts or is painful.

It comes from the verb doler, which means to hurt or to cause pain.

So:

• La inyección duele = The injection hurts
• It can also feel like The injection is painful

Both are natural ways to understand it in English.

Because doler is the infinitive form, like to hurt in English. In a normal sentence, you usually need a conjugated form.

Here, the subject is la inyección, which is third person singular, so doler becomes duele.

Present tense of doler:

• yo duelo
• tú dueles
• él/ella/usted duele
• nosotros dolemos
• vosotros doléis
• ellos/ellas/ustedes duelen

So la inyección duele uses the correct form for a singular subject.

Because doler is a stem-changing verb in the present tense.

The o in the stem changes to ue in most forms:

• duelo
• dueles
• duele
• dolemos
• doléis
• duelen

This is a common pattern in Spanish. Similar verbs include:

• poder → puedo
• volver → vuelvo
• dormir → duermo

So duele is irregular, but in a very common and predictable way.

Because this sentence is just talking about the injection itself being painful, without saying who feels the pain.

• La inyección duele = The injection hurts / is painful
• La inyección me duele = The injection hurts me

In Spanish, doler is very often used with an indirect object pronoun:

• me duele = it hurts me
• te duele = it hurts you
• le duele = it hurts him/her/you formal

But if the person experiencing the pain is not mentioned, you can simply say La inyección duele.

Usually it means the injection in a specific context, but Spanish often uses the definite article more broadly than English does.

Depending on context, it could mean:

• The injection hurts = a particular injection
• something more general like The injection is painful

If you wanted a clearly general statement, you might also hear:

• Una inyección duele = An injection hurts
• Las inyecciones duelen = Injections hurt

So context matters.

In standard Spain Spanish, inyección is pronounced roughly like:

in-yek-THYON

More precisely:

• in- as in in
• -yec- with a y sound
• -ción with the ci sounding like th in think in most of Spain
• the stress is on the last syllable: -ción

So the stress falls on -ón:

• in-yec-ción

In much of Latin America, that ci would sound like s, but in Spain it is usually th.

It has an accent mark because the stress falls on the last syllable: -ción.

Spanish stress rules say that words ending in n, s, or a vowel are normally stressed on the second-to-last syllable unless there is a written accent. Since inyección ends in n but is stressed on the last syllable, it needs the accent mark:

• inyección

That accent tells you to stress -ón.

By itself, it is usually best translated as The injection hurts.

Spanish present tense can sometimes correspond to either:

• hurts
• is hurting

But in a simple sentence like this, English normally uses hurts unless the context strongly emphasizes something happening right now.

So the most natural translation is:

• The injection hurts

Yes, you could, but it is slightly different in tone.

• La inyección duele = The injection hurts
• La inyección es dolorosa = The injection is painful

Duele sounds more direct and natural when talking about the sensation of pain.
Es dolorosa sounds a little more descriptive or formal.

In everyday speech, duele is often the more common choice.

The subject is la inyección.

That is the thing causing the pain, and the verb agrees with it:

• la inyección = singular
• duele = third person singular

This is important because with doler, Spanish is structured differently from how English learners sometimes expect. The painful thing is the grammatical subject:

• La inyección duele = The injection hurts
• literally, the injection is the thing that hurts

So the verb matches la inyección, not the person feeling the pain.