Learn Hardcore Japanese: kintyou no tame ni atama ga itaku narimasita. - Because of nervousness, my head started to hurt.

〜から / 〜ので
- General “because,” often for neutral or logical reasons.
- e.g. 雨だから／雨なので、出かけません。
- More explanatory; often used when giving reasons or justifications.
〜のせいで
- “Because of (in a negative way), due to (someone’s/something’s fault).”
- Has a clear negative, blame-like nuance.
- e.g. 彼のせいで遅れた。 = “I was late because of him / It’s his fault.”
〜のために
- Can mean either:
  1. “for the sake of / for the benefit of”: 家族のために働く
  2. “because of / due to (a cause)” – that’s the use in this sentence.
- In the “because of” sense, it’s often a bit more formal or written-sounding than から / ので.
- Neutral; doesn’t automatically carry blame like せいで, but with negative outcomes it can feel somewhat serious/formal.

Here, 緊張のために頭が痛くなりました。 is like “I got a headache due to nervousness,” sounding slightly formal and neutral.

What is the に in ために doing? Can I drop it and just say ため?

ために is a set pattern: 〜のために. The に marks it as an adverbial phrase modifying the verb phrase that follows.

緊張のために = “because of nervousness” (modifying 頭が痛くなりました)

In everyday speech, people sometimes say 〜のため without に, especially in formal writing or set phrases, but in standard modern usage for reasons, 〜のために is very common and safest to use as a learner.

So:

緊張のために頭が痛くなりました。 ✅ (very natural)
緊張のため頭が痛くなりました。 ✅ (also OK, a bit more written/formal)

Why is 頭が marked with が? Could I use は instead?

が marks 頭 (head) as the grammatical subject of the verb phrase 痛くなりました (“became painful / started hurting”).

頭が痛くなりました。
= “(My) head started to hurt.”

You can say 頭は痛くなりました in some contexts, but the nuance changes:

頭が痛くなりました。
- Neutral description: the head is what became painful.
頭は痛くなりました。
- Puts contrast or topic-focus on 頭: “As for my head, it started to hurt (as opposed to something else).”

In this kind of cause–effect sentence, 頭が痛くなりました with が is the most natural basic form.

Why is it 痛く and not 痛い? What does 痛く mean?

痛い is an い-adjective (“painful, sore”).
When you use い-adjectives with certain verbs like なる (“to become”), you change 〜い to 〜く:

痛い → 痛く
高い → 高く
寒い → 寒く

い-adjective + なる expresses “become X”:

痛くなる = to become painful / to start to hurt
高くなる = to become expensive / higher
寒くなる = to get cold

So 痛く here is the 連用形 (adverb-like form) of 痛い, used before なりました:

痛くなりました = “became painful,” “started to hurt.”

What exactly does なりました mean here? How is it different from just saying 痛かった?

なる means “to become / to turn into.”

なりました is the past polite form of なる: “became / got / turned.”

So:

痛くなりました。
- Focuses on the change of state: it became painful, it started to hurt.
痛かったです。
- Simple past state: “It hurt / it was painful.”
- Does not clearly highlight the moment of change.

In this context:

緊張のために頭が痛くなりました。
= “Because I was nervous, my head started to hurt / got a headache.”
(Shows that nervousness caused a change: from not hurting → hurting.)

Where is “I” in this sentence? How do we know it means my head?

Japanese often omits pronouns like “I,” “you,” “he,” “she” when they are clear from context.

頭が痛くなりました。 literally is “The head became painful.”
In real conversation, context makes it obvious we’re talking about the speaker’s head, so it’s understood as:
- “My head started to hurt.”

If you really need to state it explicitly, you could say:

私は緊張のために頭が痛くなりました。
But in natural Japanese, 私は would usually be omitted unless you’re contrasting yourself with someone else.

Can I change the word order, like 頭が緊張のために痛くなりました?

Yes, that word order is grammatical:

緊張のために頭が痛くなりました。
頭が緊張のために痛くなりました。

Both can work. The standard, smoother version is usually:

緊張のために頭が痛くなりました。

Putting 緊張のために at the beginning clearly sets up the cause first (“Because of nervousness, …”), which matches English flow as well.

Could I say 緊張して頭が痛くなりました instead of 緊張のために? What’s the difference?

Yes, you can say:

緊張して頭が痛くなりました。

Here:

緊張して = “being nervous / because I was nervous”
(literally, “doing nervousness and then…”)

Differences in nuance:

緊張のために頭が痛くなりました。
- A bit more formal or written-sounding.
- Explicitly marks 緊張 as the cause using a reason expression 〜のために.
緊張して頭が痛くなりました。
- More colloquial, spoken-feeling.
- The cause is shown by chaining actions/states with 〜て (“being nervous and then my head started hurting”).

Both are correct; 緊張して〜 is very common in conversation.

What’s the difference between 緊張のために and 緊張のせいで in this sentence?

You could say:

緊張のせいで頭が痛くなりました。

Both mean the nervousness caused the headache, but:

〜のせいで
- Stronger negative nuance; “because of / it’s the fault of ~.”
- Emphasizes that this cause is bothersome or undesirable.
〜のために
- More neutral or formal. Can be used with both positive and negative outcomes, though with negative ones it can still sound somewhat serious.

So:

緊張のために頭が痛くなりました。
= My head started to hurt due to nervousness. (neutral/formal-ish)
緊張のせいで頭が痛くなりました。
= My head started to hurt because of (that damn) nervousness. (more clearly negative/blaming tone)

Is this sentence polite or casual? How would I say it in casual speech?

緊張のために頭が痛くなりました。 is in polite past form because of なりました.

Casual equivalents:

緊張のために頭が痛くなった。
Or more colloquially: 緊張して頭が痛くなった。
Or with blame nuance: 緊張のせいで頭が痛くなった。

All of these are casual, used with friends or in informal writing.

Does 痛くなりました mean “got a headache” or literally “my head became painful”? Which is more natural in English?

Literally:

頭が痛くなりました。 = “My head became painful.”

Natural English translation depends on style:

Everyday English: “I got a headache.”
Slightly more literal: “My head started to hurt.”

Both convey the same idea and match the Japanese nuance of a change of state (not hurting → hurting).
“Got a headache” is usually the smoothest translation in natural English.