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Netsu Meaning in Japanese: How to Say “I Have a Fever”

Japanese

Hello, I’m Kodak.

 

If you become sick while traveling or living in Japan, one of the most useful words to know is 熱 (netsu).

In a medical context, 熱 means “fever”, and the most common way to say “I have a fever” is:

熱ねつがあります。
Netsu ga arimasu.
I have a fever.

 

Learner
Does netsu always mean “fever”?
Kodak
Not always. 熱 can also mean heat, passion, or enthusiasm.

However, in expressions such as 熱がある and 熱が出る, it normally means a fever.

 

The three expressions to learn first

熱があります。
Netsu ga arimasu.
I have a fever.

熱が出ました。
Netsu ga demashita.
I developed a fever.

熱はありますか？
Netsu wa arimasu ka?
Do you have a fever?

 

In this article, you will learn:
① what 熱 (netsu) means
② how to say “I have a fever” naturally
③ the difference between 熱がある and 熱が出る
④ how to say your temperature in Japanese
⑤ useful phrases for a doctor, clinic, pharmacy, or hotel
⑥ the differences between 熱, 発熱, 熱い, 暑い, and 熱っぽい
⑦ natural example sentences and short conversations

 

Contents

What Does 熱 (Netsu) Mean in Japanese?

Kanji: 熱
Hiragana: ねつ
Romaji: netsu
Part of speech: noun
Main meanings: heat; fever; passion; enthusiasm

 

When talking about illness, 熱 means a body temperature that is higher than normal: a fever.

熱があります。
Netsu ga arimasu.
I have a fever.

昨日から熱があります。
Kinō kara netsu ga arimasu.
I have had a fever since yesterday.

The same kanji can mean ordinary heat in other contexts.

この機械は熱を出します。
Kono kikai wa netsu o dashimasu.
This machine produces heat.

It can also refer to enthusiasm or intense interest.

サッカー熱が高まっています。
Sakkā-netsu ga takamatte imasu.
Enthusiasm for soccer is growing.

Learner
How do I know whether 熱 means “heat” or “fever”?
Kodak
Look at the surrounding words and situation.

At a clinic, 熱があります clearly means “I have a fever.”

When discussing a machine, cooking, or energy, 熱 usually means physical heat.

 

Pronunciation of 熱 (Netsu)

Japanese: 熱
Reading: ねつ
Romaji: netsu
Mora: ね・つ (2 morae)

 

The final つ (tsu) should remain audible, although its vowel may sound light in natural speech. Avoid pronouncing netsu as simply “nets.”

Learner
Is it pronounced like the English word “nets”?
Kodak
It may sound similar at first, but Japanese ねつ has two clear morae: ね・つ.

Keep a short u-like ending in つ rather than ending with a strong English s.

 

How to Say “I Have a Fever” in Japanese

The standard expression is:

熱 + が + あります

熱 = fever
が = particle marking what exists or is present
あります = exists; there is; have

 

熱があります。
Netsu ga arimasu.
I have a fever.

A very literal translation would be “A fever exists,” but the natural English translation is “I have a fever.”

Learner
Where is the Japanese word for “I”?
Kodak
Japanese often omits the subject when it is obvious.

If you are describing your own symptoms, 熱があります naturally means “I have a fever.” You do not need to begin every sentence with 私は.

 

Polite and Casual Forms

熱があります。
Netsu ga arimasu.
I have a fever. — polite

熱がある。
Netsu ga aru.
I have a fever. — plain form

熱ある？
Netsu aru?
Do you have a fever? — very casual; particle omitted

熱はないです。
Netsu wa nai desu.
I do not have a fever.

 

熱がある vs 熱が出る: What Is the Difference?

Both expressions are common, but they focus on different parts of the situation.

熱がある (netsu ga aru)
A fever is present now.
⇒ have a fever

熱が出る (netsu ga deru)
A fever appears or develops.
⇒ develop a fever / come down with a fever / run a fever

 

今、熱があります。
Ima, netsu ga arimasu.
I have a fever now.

昨夜、熱が出ました。
Sakuya, netsu ga demashita.
I developed a fever last night.

Learner
Can I say 昨日から熱が出ました?
Kodak
Japanese speakers will understand it, but the focus is clearer if you choose one of these:

昨日、熱が出ました。
I developed a fever yesterday.

昨日から熱があります。
I have had a fever since yesterday.

 

Other Useful Forms of 熱が出る

熱が出ました。
I developed a fever.

熱が出ています。
I am running a fever.

熱が出そうです。
I feel like I may develop a fever.

また熱が出ました。
My fever came back. / I developed a fever again.

 

How to Ask “Do You Have a Fever?”

Two common questions are 熱はありますか and 熱がありますか.

熱はありますか？
Netsu wa arimasu ka?
Do you have a fever?

熱がありますか？
Netsu ga arimasu ka?
Do you have a fever?

 

Both are natural. In a medical interview, 熱はありますか often treats “fever” as the symptom currently being checked, while 熱がありますか asks more neutrally whether a fever is present.

Learner
Do I need to master the difference between は and が before using this phrase?
Kodak
No. As a beginner, memorize 熱はありますか？ as a useful question and 熱があります as a useful answer.

You can study the finer particle difference later.

 

How to Say Your Temperature in Japanese

In Japan, temperatures are normally given in degrees Celsius.

38度の熱があります。
Sanjū-hachi-do no netsu ga arimasu.
I have a fever of 38 degrees Celsius.

熱は38度です。
Netsu wa sanjū-hachi-do desu.
My temperature is 38 degrees Celsius.

体温は38度です。
Taion wa sanjū-hachi-do desu.
My body temperature is 38 degrees Celsius.

 

Learner
Which sentence is easiest to use at a clinic?
Kodak
熱は38度です is short and easy.

You can also show the number on your thermometer or phone while saying 38度です.

 

Useful Temperature Vocabulary

体温 (taion)
body temperature

平熱 (heinetsu)
normal body temperature

微熱 (binetsu)
a slight or low-grade fever

高熱 (kōnetsu)
a high fever

体温計 (taionkei)
thermometer

 

平熱は36度5分くらいです。
Heinetsu wa sanjū-roku-do go-bu kurai desu.
My normal temperature is about 36.5 degrees Celsius.

少し微熱があります。
Sukoshi binetsu ga arimasu.
I have a slight fever.

高熱が続いています。
Kōnetsu ga tsuzuite imasu.
My high fever has continued.

 

Useful Verbs Used with 熱

1. 熱を測る: To Take Your Temperature

熱を測りました。
Netsu o hakarimashita.
I took my temperature.

体温を測ってください。
Taion o hakatte kudasai.
Please take your temperature.

体温を測る is the more literal and precise expression, while 熱を測る is common in everyday conversation.

2. 熱が上がる: The Fever Goes Up

夜になると熱が上がります。
Yoru ni naru to netsu ga agarimasu.
My fever goes up at night.

3. 熱が下がる: The Fever Goes Down

薬を飲んだら熱が下がりました。
Kusuri o nondara netsu ga sagarimashita.
My fever went down after I took the medicine.

4. 熱が続く: The Fever Continues

三日間、熱が続いています。
Mikka-kan, netsu ga tsuzuite imasu.
My fever has continued for three days.

5. 熱がぶり返す: The Fever Returns

一度下がった熱がぶり返しました。
Ichido sagatta netsu ga burikaeshimashita.
My fever went down once, but then came back.

 

熱がある vs 熱っぽい: Fever vs Feeling Feverish

熱がある
You have a measured or recognized fever.
⇒ I have a fever.

熱っぽい
You feel as though you may have a fever.
⇒ I feel feverish.

 

少し熱っぽいです。
Sukoshi netsuppoi desu.
I feel a little feverish.

熱っぽいですが、まだ体温は測っていません。
Netsuppoi desu ga, mada taion wa hakatte imasen.
I feel feverish, but I have not taken my temperature yet.

Learner
So should I say 熱っぽい if I have not used a thermometer?
Kodak
That is a useful distinction.

If you only feel hot, tired, or feverish, 熱っぽいです is natural. If you know that you have a fever, use 熱があります.

 

熱 vs 発熱: What Is the Difference?

熱 is the everyday word, while 発熱 (hatsunetsu) is more formal and medical.

熱 (netsu)
Everyday conversation
⇒ fever; heat

発熱 (hatsunetsu)
Medical, formal, or written language
⇒ fever; developing an elevated body temperature

 

熱があります。
Netsu ga arimasu.
I have a fever.

昨日から発熱しています。
Kinō kara hatsunetsu shite imasu.
I have had a fever since yesterday.

発熱の症状があります。
Hatsunetsu no shōjō ga arimasu.
I have symptoms of fever.

Learner
Which one should I use when speaking to a doctor?
Kodak
熱があります is completely natural and easier for beginners.

You may see 発熱 on hospital forms, notices, medicine information, and official instructions.

 

熱, 熱い, and 暑い: Do Not Confuse These Words

Japanese Reading Meaning Example
熱 netsu heat; fever 熱があります。
熱い atsui hot to the touch; physically hot お茶が熱いです。
暑い atsui hot weather or a hot environment 今日は暑いです。

 

熱があります。
I have a fever.

体が熱いです。
My body feels hot.

今日は暑いです。
It is hot today.

このスープは熱いです。
This soup is hot.

 

Learner
If I say 暑いです at a hospital, will it mean “I have a fever”?
Kodak
Usually not. 暑いです means that you feel hot because of the room, weather, clothing, or environment.

To clearly say you have a fever, use 熱があります.

 

How to Describe a Fever at a Doctor or Clinic

You do not need a long sentence. Giving four pieces of information is often enough:

① Symptom — 熱があります
② When it started — 昨日からです
③ Temperature — 38度です
④ Other symptoms — のども痛いです

 

Simple Model Answer

昨日から熱があります。今朝は38度でした。のども痛いです。
Kinō kara netsu ga arimasu. Kesa wa sanjū-hachi-do deshita. Nodo mo itai desu.
I have had a fever since yesterday. It was 38 degrees this morning. My throat also hurts.

Learner
That sentence still feels difficult to remember.
Kodak
Then say it in short pieces:

熱があります。
I have a fever.

昨日からです。
Since yesterday.

38度です。
It is 38 degrees.

Short, clear sentences are completely acceptable.

 

Doctor–Patient Conversation Using 熱

Doctor
どうしましたか？
Dō shimashita ka?
What seems to be the problem?
Patient
昨日から熱があります。
Kinō kara netsu ga arimasu.
I have had a fever since yesterday.
Doctor
何度くらいですか？
Nando kurai desu ka?
About how high is your temperature?
Patient
今朝は38度2分でした。
Kesa wa sanjū-hachi-do ni-bu deshita.
It was 38.2 degrees this morning.
Doctor
ほかに症状はありますか？
Hoka ni shōjō wa arimasu ka?
Do you have any other symptoms?
Patient
せきと、のどの痛みがあります。
Seki to, nodo no itami ga arimasu.
I have a cough and a sore throat.

 

Useful Fever Phrases for Travel in Japan

熱があります。
I have a fever.

昨日、熱が出ました。
I developed a fever yesterday.

少し熱っぽいです。
I feel a little feverish.

熱は38度です。
My temperature is 38 degrees Celsius.

熱が下がりません。
My fever will not go down.

熱が上がってきました。
My fever is getting higher.

熱が三日間続いています。
My fever has continued for three days.

体温計はありますか？
Do you have a thermometer?

近くに病院はありますか？
Is there a hospital nearby?

英語を話せる医師はいますか？
Is there a doctor who speaks English?

 

Mini Conversations in Different Situations

At a Hotel

Guest
すみません。熱があります。
Sumimasen. Netsu ga arimasu.
Excuse me. I have a fever.
Staff
病院をお探しですか？
Byōin o osagashi desu ka?
Are you looking for a hospital?

At a Pharmacy

Customer
熱があって、のども痛いです。
Netsu ga atte, nodo mo itai desu.
I have a fever, and my throat hurts too.
Pharmacist
熱は何度ですか？
Netsu wa nando desu ka?
What is your temperature?

Calling Work

Employee
今朝から熱があるので、今日は休ませてください。
Kesa kara netsu ga aru node, kyō wa yasumasete kudasai.
I have had a fever since this morning, so please allow me to take the day off.

 

Common Beginner Mistakes

Mistake 1: Saying 熱いです for “I Have a Fever”

△ 熱いです。
Something feels hot, or my body feels hot.

○ 熱があります。
I have a fever.

Mistake 2: Using 暑い for Illness

暑いです。
I feel hot because of the weather or environment.

熱があります。
I have a fever.

Mistake 3: Always Adding 私は

私は熱があります is grammatically possible, but 熱があります is usually more natural when the context already shows that you are talking about yourself.

Mistake 4: Confusing 熱がある and 熱が出た

Use 熱がある for the present condition and 熱が出た for the moment or event of developing a fever.

Mistake 5: Saying a Decimal as a Point

In everyday Japanese, 38.2°C may be said as 38度2分 (sanjū-hachi-do ni-bu). Saying 38.2度 is also understood, especially when reading a digital display, but learning the 度・分 pattern is useful in medical conversations.

 

Natural Example Sentences with 熱

朝から少し熱があります。
Asa kara sukoshi netsu ga arimasu.
I have had a slight fever since this morning.

昨日の夜、急に熱が出ました。
Kinō no yoru, kyū ni netsu ga demashita.
I suddenly developed a fever last night.

熱は何度ありますか？
Netsu wa nando arimasu ka?
How high is your temperature?

今は37度8分です。
Ima wa sanjū-nana-do hachi-bu desu.
It is 37.8 degrees now.

薬を飲んでも熱が下がりません。
Kusuri o nonde mo netsu ga sagarimasen.
My fever does not go down even after taking medicine.

夜になると熱が上がります。
Yoru ni naru to netsu ga agarimasu.
My fever rises at night.

熱は下がりましたが、まだだるいです。
Netsu wa sagarimashita ga, mada darui desu.
My fever has gone down, but I still feel weak.

熱があって、せきも出ます。
Netsu ga atte, seki mo demasu.
I have a fever and a cough.

子どもに高い熱があります。
Kodomo ni takai netsu ga arimasu.
My child has a high fever.

熱っぽいので、体温を測ります。
Netsuppoi node, taion o hakarimasu.
I feel feverish, so I will take my temperature.

 

FAQ About Netsu and Fever in Japanese

What does netsu mean in Japanese?

熱 (netsu) means heat. In a medical context, it means a fever. It can also refer figuratively to passion or enthusiasm.

How do you say “fever” in Japanese?

The everyday Japanese word for fever is 熱 (netsu). The more formal or medical word is 発熱 (hatsunetsu).

How do you say “I have a fever” in Japanese?

Say 熱があります (netsu ga arimasu). The casual plain form is 熱がある (netsu ga aru).

What does netsu ga aru mean?

熱がある literally states that a fever is present. Its natural English meaning is “to have a fever.”

What is the difference between netsu ga aru and netsu ga deru?

熱がある describes the current state of having a fever. 熱が出る describes a fever appearing or developing.

How do I ask someone if they have a fever?

Say 熱はありますか？ (netsu wa arimasu ka?) or 熱がありますか？ (netsu ga arimasu ka?).

How do I say “I feel feverish” in Japanese?

Say 熱っぽいです (netsuppoi desu).

What is the difference between netsu and hatsunetsu?

熱 is the common everyday word. 発熱 is more formal and is common in medical writing, notices, and hospital forms.

Does atsui mean “I have a fever”?

No. 暑い usually means the weather or environment feels hot, while 熱い describes something physically hot. To say “I have a fever,” use 熱があります.

How do I say my temperature in Japanese?

You can say 熱は38度です or 体温は38度です, meaning “My temperature is 38 degrees Celsius.”

 

Which 熱 Phrase Matches Your Situation?

Answer two quick questions about your fever.

Q1. Have you actually measured your temperature?
No, it is just a feeling → 熱っぽいです
I feel feverish – not yet confirmed
Yes, it is confirmed → 熱があります
I have a fever – a measured, recognized fever
Q2. What is the fever doing right now?
It just started → 熱が出ました
I developed a fever
It is climbing → 熱が上がっています
My fever is going up
It is dropping → 熱が下がりました
My fever went down
It has lasted for days → 熱が続いています
My fever has continued
It came back after going down → 熱がぶり返しました
My fever returned

※ 熱 alone can mean heat, passion, or fever – it is the verb around it (ある, 出る, 上がる, 下がる) that tells the listener you mean a fever, and which stage it is at.

Summary: Netsu Meaning and How to Say “I Have a Fever”

● 熱 (netsu)
Means heat and, in a medical context, fever.

● 熱があります。
I have a fever.

● 熱が出ました。
I developed a fever.

● 熱はありますか？
Do you have a fever?

● 熱っぽいです。
I feel feverish.

● 熱が上がる / 熱が下がる
The fever goes up / the fever goes down.

● 発熱 (hatsunetsu)
A more formal or medical word for fever.

● Do not confuse them
熱 = heat or fever
熱い = physically hot
暑い = hot weather or environment

 

Kodak
For your first step, remember just one sentence:

熱があります。

Even if you cannot explain every detail, this phrase clearly tells a Japanese speaker that you have a fever.

 

Language note: This article explains Japanese vocabulary and communication. It does not diagnose illness or replace medical advice. When you are concerned about your symptoms, seek guidance from an appropriate medical professional.

 

References

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