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発熱する

B1 verb #4,500 most common 7 min read

発熱する

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Practice it Examples Notes & Tips 発熱する in 30 Seconds

Explanation 発熱する in your Level:

At the A1 level, you don't need to use 'hatsunetsu suru' often. It is a bit difficult because it uses two kanji. Instead, you usually learn 'netsu' (fever) and 'deru' (to come out). However, you might see '発熱' (hatsunetsu) on signs at airports or stores where they check your temperature. Just remember: hatsu (start/emit) + netsu (heat) = fever starting. If you see this word, it means someone is sick with a temperature.

At the A2 level, you should recognize '発熱する' as a formal way to say 'to have a fever.' You will encounter it in health-related reading passages or when listening to formal news. It is a 'suru-verb,' so it follows the same rules as 'benkyo suru' or 'kaimono suru.' You might use it in a formal email to a teacher: 'Kinou hatsunetsu shimashita' (I had a fever yesterday). It sounds more polite than the casual 'netsu ga deta.'

For B1 learners, '発熱する' is a key vocabulary item for medical and professional situations. You should be able to use it to describe symptoms precisely. It is often used in the 'te-iru' form (hatsunetsu shite iru) to describe a current state. You should also know related words like 'binetsu' (slight fever) and 'kounetsu' (high fever). Understanding the difference between clinical 'hatsunetsu' and casual 'netsu' is important for maintaining the correct register in your Japanese speech.

At the B2 level, you should be comfortable with '発熱' in scientific or sociological contexts. For example, discussing the 'hatsunetsu-hanno' (exothermic reaction) in a science context or 'hatsunetsu-gairai' (fever clinics) in a social context. You should also understand its use in passive-like structures or as a noun modified by adjectives. You'll notice it in formal reports about public health or pharmaceutical trials where precision is required.

C1 learners should master the nuances of '発熱する' compared to its synonyms in academic writing. You should understand how it functions in complex sentences, such as 'hatsunetsu o tomonau' (accompanied by a fever). You should also be aware of its metaphorical uses in older literature, though in modern Japanese, it is almost exclusively physical. You should be able to discuss the physiological mechanism of fever using this term in a formal presentation.

At the C2 level, you should have a native-like grasp of '発熱する,' including its etymological roots and its role in the Japanese medical lexicon. You should be able to distinguish between 'hatsunetsu' (the symptom) and 'netsubyo' (feverish illness) in historical texts. You can use the term fluently in medical discourse, legal documents regarding health safety, and high-level academic discussions about thermoregulation.

Practice it Examples Notes & Tips

発熱する in 30 Seconds

Formal verb for having/getting a fever.
Common in hospitals, news, and official health forms.
Standard 'suru' verb conjugation (Class 3).
Can also refer to scientific heat generation (exothermic).

The Japanese verb 発熱する (hatsunetsu suru) is a formal and clinical way to describe the physiological process of developing or having a fever. While English speakers might simply say 'I have a temperature' or 'I'm running a fever,' Japanese distinguishes between the casual state and the medical occurrence. The word is composed of two kanji: 発 (hatsu) meaning 'to emit, discharge, or occur' and 熱 (netsu) meaning 'heat' or 'fever.' Together with the light verb する (suru), it functions as a functional verb meaning 'to manifest a fever.'

Clinical Register: This term is predominantly used in medical contexts, news reports, and official documentation. If you are filling out a health check form at a Japanese school or office, you will see this word rather than the more casual 'netsu ga deru.'
Biological Process: It refers specifically to the body's internal temperature rising above the normal range as a response to infection or inflammation.

ワクチンを接種した後に、多くの人が一時的に発熱することがあります。
(After receiving the vaccine, many people may temporarily develop a fever.)

In daily conversation, '発熱する' can feel a bit stiff. If you are telling a friend you feel sick, you would likely say '熱が出た' (netsu ga deta). However, in the era of global pandemics, '発熱' has become a common household word because of its use in temperature screening protocols. You will often see signs saying '発熱のある方は入場をお控えください' (Those with a fever, please refrain from entering).

昨夜から息子が発熱しており、今日は学校を休みます。
(My son has been running a fever since last night, so he will be absent from school today.)

The word also appears in scientific contexts outside of human health. For instance, chemical reactions that release heat are called '発熱反応' (exothermic reactions). This highlights that the core meaning is the 'generation of heat.' Understanding this broader context helps learners realize why it feels more 'scientific' than the colloquial 'netsu' (heat/fever).

Social Context: In Japan, managing a fever is a serious social responsibility. Reporting a 'hatsunetsu' is often the primary reason for self-isolation or seeking medical testing.

Using 発熱する correctly involves understanding its grammar as a 'Suru-Verb' (Class 3 verb). It follows standard conjugation patterns but is almost always used in the context of health conditions. Since it is a self-occurring physiological phenomenon, it does not typically take a direct object with 'o'. Instead, the person who has the fever is the subject marked by 'ga' or 'wa'.

患者は急に発熱した。
(The patient suddenly developed a fever.)

When describing a continuous state, you use the 'te-iru' form: 発熱している (hatsunetsu shite iru). This means 'is currently running a fever.' This is the most common form in medical interviews.

Past Tense Usage: '発熱しました' (hatsunetsu shimashita) is used to report when the fever started. It implies the event of the temperature rising.
Conditional Usage: '発熱した場合は' (hatsunetsu shita baai wa) - 'In the event of a fever.' This is ubiquitous on medication instructions and event guidelines.

もし発熱したら、すぐに連絡してください。
(If you develop a fever, please contact us immediately.)

One subtle point: while 'netsu ga deru' emphasizes the fever 'coming out' (appearing), 'hatsunetsu suru' sounds like the body is actively 'generating heat.' Therefore, in a report about a group of people, 'hatsunetsu-sha' (people with fever) is the standard term. You won't hear 'netsu ga deru hito' in a news broadcast about a flu outbreak.

乳幼児は夜間に発熱しやすい。
(Infants and toddlers tend to develop fevers easily at night.)

In business emails, if you are calling out sick, use the noun form for brevity: '発熱のため、本日欠勤いたします' (Due to fever, I will be absent today). Here, 'hatsunetsu' acts as the reason. This is considered more professional than using the verb phrase in a long sentence.

You will encounter 発熱する in several specific environments in Japan. Understanding these contexts helps you recognize the level of formality and the gravity of the situation being discussed. It is rarely used when joking or in lighthearted casual speech.

The Hospital or Clinic: When a nurse asks, 'いつから発熱しましたか？' (Since when have you had a fever?), they are looking for a clinical timeline. You would respond using the same verb or the noun 'hatsunetsu.'
News and Public Announcements: During flu season, NHK news will report on the number of 'hatsunetsu-kanja' (fever patients). They will use '発熱する' to describe the symptoms of a new virus strain.

「入口で検温を行います。発熱している方は入場をお断りします。」
(Temperature checks will be conducted at the entrance. Those running a fever will be denied entry.)

School environments are another major site for this word. Teachers keep a 'health diary' (kenko kansatsu) for their students. If a child looks unwell, the teacher might say, '発熱があるみたいですね' (It seems you have a fever). Note that here the noun 'hatsunetsu' is used with 'aru' (to have), which is a common variation of the verb usage.

In the workplace, 'hatsunetsu' is the standard terminology for HR reports. If you say 'netsu ga deta,' it sounds like you're talking to a family member. If you write in a Slack channel, '発熱があるため、本日はリモートワークに切り替えます' (Because I have a fever, I will switch to remote work today), it sounds responsible and clear.

「ワクチン接種の翌日に発熱するのは副反応の一つです。」
(Developing a fever the day after vaccination is one of the side effects.)

While 発熱する is straightforward, English learners often make nuance-related errors or confuse it with adjectives. Here are the most common pitfalls to avoid.

Confusing with 'Atsui' (Hot): Do not say 'I am hatsunetsu' (私は発熱です). While 'hatsunetsu' is a noun, you must use the verb form 'hatsunetsu shite iru' to describe your state. Also, 'atsui' (暑い/熱い) means the weather or an object is hot, not that you have a fever.
Using the Wrong Particle: Avoid 'Netsu o hatsunetsu suru.' This is redundant (like saying 'to fever a fever'). Use 'hatsunetsu suru' alone or 'netsu ga deru.'

Incorrect: 彼は発熱をしました。(He did a fever.)
Correct: 彼は発熱しました。(He developed a fever.)

Another mistake is overusing 'hatsunetsu suru' in casual situations. If you tell your Japanese roommate 'hatsunetsu shimashita,' they might think you are speaking like a medical textbook. For close friends, stick to 'netsu ga deta' (a fever came out) or 'netsu ga aru' (I have a fever).

Wait, there's more! Don't use 'hatsunetsu suru' for feeling 'heated' in an emotional sense (like being angry or excited). For that, Japanese uses 'atsuku naru' or 'kofun suru.' 'Hatsunetsu' is strictly physical temperature.

「昨日は発熱したので、ジムに行けませんでした。」
(I couldn't go to the gym yesterday because I had a fever.) - *This is a correct, slightly formal usage.*

Japanese has several ways to talk about fevers and heat. Choosing the right one depends on how high the fever is and who you are talking to.

熱が出る (Netsu ga deru): The most natural, everyday way to say 'to get a fever.' It literally means 'the fever comes out.' Use this with friends and family.
微熱がある (Binetsu ga aru): To have a slight fever or a 'low-grade' fever. Usually refers to a temperature just slightly above normal (e.g., 37.0°C - 37.4°C).
高熱が出る (Kounetsu ga deru): To have a high fever. This is used when the temperature is significantly high (e.g., 38.5°C or higher).

「ただの微熱だと思っていたら、夜に高熱に変わりました。」
(I thought it was just a slight fever, but it turned into a high fever at night.)

There is also the term 解熱 (genetsu), which means the fever going down. A 'genetsuzai' (解熱剤) is a fever reducer like ibuprofen or paracetamol. If you are 'hatsunetsu shite iru,' you might need a 'genetsuzai.'

In summary, while 'hatsunetsu suru' is the verb for 'developing a fever,' you should match your word choice to the context. In a medical report, use '発熱.' In a text to your mom, use '熱が出た.'

How Formal Is It?

Fun Fact

In the Edo period, fevers were often called 'netsubyo' (heat illness). The term 'hatsunetsu' became more common as modern medicine was adopted and standardized terminology was needed.

Pronunciation Guide

UK /hætsuːnɛtsuː suːruː/

US /hɑtsunɛtsu suru/

The primary stress in Japanese is pitch-based. In 'hatsunetsu,' the pitch stays relatively flat (Heiban style) or starts low and rises.

Rhymes With

Kousetsu (snowfall) Ketsuretsu (breakdown) Setsu (theory) Betsu (different) Tetsu (iron) Zetsu (tongue) Netsu (heat) Hatsu (departure)

Common Errors

Pronouncing 'tsu' as 'tu'.
Stress on the wrong syllable (Japanese is mora-timed).
Blending 'hatsu' and 'netsu' too quickly; keep the 'n' distinct.
Over-emphasizing the 'u' at the end of 'suru'.
Confusing the pitch with 'hatsumei' (invention).

Difficulty Rating

Reading 3/5

Kanji are common but require knowledge of Kango compounds.

Writing 4/5

Writing 'hatsu' (発) can be tricky for beginners.

Speaking 2/5

Pronunciation is straightforward.

Listening 3/5

Needs to be distinguished from similar sounding words like 'hatsumei'.

What to Learn Next

Prerequisites

熱 (Netsu) 出る (Deru) する (Suru) 体 (Karada) 病気 (Byouki)

Learn Next

症状 (Symptoms) 診断 (Diagnosis) 治療 (Treatment) 副作用 (Side effects) 安静 (Rest)

Advanced

免疫 (Immunity) 炎症 (Inflammation) 感染 (Infection) 抗体 (Antibody) 恒温動物 (Homeotherm)

Grammar to Know

Suru-Verbs (Noun + Suru)

勉強する、発熱する。

Te-iru for State

発熱している (Currently having a fever).

Node/Kara for Reason

発熱したので休みます。

Baai (In case of)

発熱した場合は連絡してください。

Yasui (Easy to/Prone to)

子供は発熱しやすい。

Examples by Level

熱があります。

I have a fever.

A1 alternative to hatsunetsu suru.

発熱、ありますか？

Do you have a fever?

Noun use.

昨日、発熱しました。

Yesterday, I had a fever.

Past tense.

発熱は怖いです。

A fever is scary.

Noun subject.

発熱していますか？

Are you running a fever?

Present progressive.

はい、発熱しています。

Yes, I am running a fever.

Short response.

発熱したら、寝てください。

If you get a fever, please sleep.

Conditional 'tara'.

発熱がないです。

I don't have a fever.

Negative state.

急に発熱して、びっくりしました。

I was surprised because I suddenly got a fever.

Te-form for reason.

発熱した時は、水をたくさん飲んでください。

When you have a fever, please drink a lot of water.

Toki (when) structure.

子供が夜中に発熱しました。

The child developed a fever in the middle of the night.

Past tense.

発熱がある人は、ここに入れません。

People with a fever cannot enter here.

Relative clause.

昨日からずっと発熱しています。

I have had a fever since yesterday.

Continuous state.

発熱のせいで、頭が痛いです。

My head hurts because of the fever.

Noun + no sei de (because of).

彼は発熱しやすい体質です。

He has a constitution that easily develops fevers.

-yasui (easy to).

発熱したので、仕事を休みます。

I'm taking off work because I developed a fever.

Node (because).

もし発熱した場合は、この薬を飲んでください。

In case you develop a fever, please take this medicine.

Baai (in the event of).

患者が発熱した原因を調べています。

We are investigating the cause of the patient's fever.

Noun modification.

ワクチンを打った後、一時的に発熱することがあります。

After getting the vaccine, you may temporarily develop a fever.

Koto ga aru (there are times when).

発熱している間は、外出を控えてください。

While you have a fever, please refrain from going out.

Aida (while).

38度以上の発熱が続いています。

A fever of 38 degrees or higher is continuing.

Ga tsuzuite iru (is continuing).

発熱していても、食欲はあります。

Even though I have a fever, I have an appetite.

Te-ite mo (even if/though).

学校で発熱した生徒が数名出ました。

Several students at school developed fevers.

Past tense reporting.

インフルエンザにかかると、急激に発熱します。

When you catch the flu, you develop a fever rapidly.

Adverbial usage (kyugeki ni).

この病気は、発熱と咳を主な症状とします。

This disease has fever and coughing as its main symptoms.

Formal description.

発熱の初期段階では、寒気を感じることが多いです。

In the early stages of a fever, one often feels chills.

Noun phrase.

激しい運動の後に発熱するケースも報告されています。

Cases of developing a fever after intense exercise have also been reported.

Case report style.

発熱を伴う発疹が見られたら、すぐに受診してください。

If a rash accompanied by a fever is seen, please see a doctor immediately.

Tomonau (accompanying).

抗生物質の投与により、発熱が治まりました。

The fever subsided due to the administration of antibiotics.

Formal cause/effect.

発熱している患者を隔離する必要があります。

It is necessary to isolate patients who are running a fever.

Necessity structure.

彼は発熱を理由に会議を欠席した。

He was absent from the meeting citing a fever as the reason.

Riyu ni (as the reason).

化学反応によって、溶液が発熱した。

The solution generated heat due to a chemical reaction.

Scientific usage.

体内の免疫システムが異物と戦う際に発熱する仕組みを解説します。

I will explain the mechanism by which the body develops a fever when the immune system fights foreign substances.

Explanatory tone.

原因不明の発熱が数週間続く「不明熱」の診断は困難を極める。

Diagnosing 'fever of unknown origin,' where a fever of unknown cause lasts for several weeks, is extremely difficult.

Technical medical term.

その物質は湿気に触れると激しく発熱する性質がある。

That substance has the property of generating intense heat when it comes into contact with moisture.

Scientific property description.

術後の経過は良好だが、稀に再発熱することがある。

The post-operative progress is good, but in rare cases, a recurrent fever may occur.

Prefix 'sai-' (re-).

心理的なストレスが原因で発熱する「心因性発熱」も存在する。

There is also 'psychogenic fever,' where a fever is caused by psychological stress.

Psychological terminology.

発熱という生体防御反応を無理に薬で抑えるべきではないという意見もある。

Some argue that the biological defense response known as fever should not be forcibly suppressed with medication.

Complex argumentative structure.

局所的な発熱は、炎症の典型的な兆候である。

Localized heat is a typical sign of inflammation.

Academic observation.

患者の発熱パターンを記録し、病気の特定に役立てる。

Record the patient's fever patterns to help identify the disease.

Clinical procedure.

発熱機序の解明は、感染症治療における重要な一歩となる。

Elucidating the mechanism of fever generation will be an important step in the treatment of infectious diseases.

Highly technical noun compounds.

その古文書には、都で原因不明の発熱が流行し、多くの命が失われたと記されている。

The ancient document records that an unexplained fever spread through the capital, leading to many deaths.

Historical narrative.

中枢神経系の損傷により、体温調節機能が麻痺し、異常に発熱する場合がある。

Damage to the central nervous system may paralyze thermoregulation, leading to abnormal fever.

Physiological detail.

この合金は特定の条件下で自己発熱する特性を持ち、産業利用が期待されている。

This alloy has the property of self-heating under specific conditions and is expected to be used in industry.

Industrial/Scientific context.

発熱という現象を多角的に分析することで、生命の神秘に迫る。

By analyzing the phenomenon of fever from multiple perspectives, we approach the mystery of life.

Philosophical/Scientific inquiry.

劇症型の感染症においては、発熱から死に至るまでの時間が極めて短い。

In fulminant infectious diseases, the time from the onset of fever to death is extremely short.

Medical urgency.

環境温度の急変に伴い、恒温動物であっても一時的に発熱に近い状態を呈することがある。

With sudden changes in environmental temperature, even homeothermic animals may temporarily exhibit conditions close to a fever.

Biological nuance.

発熱患者のスクリーニング体制を強化し、パンデミックの拡大を阻止する。

Strengthen the screening system for feverish patients to prevent the spread of the pandemic.

Public policy terminology.

Common Collocations

急に発熱する

発熱を伴う

発熱がある

一時的に発熱する

発熱が続く

発熱症状

発熱外来

発熱反応

発熱量

再発熱

Common Phrases

発熱のため欠席します

— Standard way to report absence from school or work due to fever.

本日、発熱のため欠席いたします。

37.5度以上の発熱

— The common threshold in Japan for being considered 'sick' for school/work.

37.5度以上の発熱がある場合は入場できません。

発熱の有無

— Whether or not one has a fever (used in forms).

発熱の有無を確認してください。

発熱して苦しい

— Suffering due to a fever.

発熱して苦しそうです。

発熱が引く

— The fever subsiding.

やっと発熱が引きました。

発熱の疑い

— Suspected fever.

発熱の疑いがある患者。

原因不明の発熱

— A fever with no known cause.

原因不明の発熱に悩まされる。

発熱しやすい

— Prone to getting fevers.

赤ん坊は発熱しやすい。

発熱を抑える

— To suppress or reduce a fever.

薬で発熱を抑える。

発熱を確認する

— To check for a fever.

毎朝、発熱を確認しています。

Often Confused With

発熱する vs 暑い (Atsui)

Atsui refers to weather; Hatsunetsu refers to body temperature.

発熱する vs 発明 (Hatsumei)

Hatsumei means invention; sounds similar but unrelated.

発熱する vs 熱中 (Netchu)

Netchu means being absorbed in something, not having a fever.

Idioms & Expressions

"知恵熱"

— A fever in infants thought to be caused by mental development (metaphorical/cultural).

それは知恵熱かもしれないね。

Colloquial

"熱に浮かされる"

— To be delirious with fever; also to be madly in love or obsessed.

彼は彼女に熱に浮かされている。

Literary

"熱を上げる"

— To become very enthusiastic about something or someone.

彼は新しい趣味に熱を上げている。

Common

"熱が入る"

— To become enthusiastic or earnest about a task.

練習に熱が入る。

Common

"熱弁をふるう"

— To make an impassioned speech.

政治家が熱弁をふるった。

Formal

"熱が冷める"

— To lose interest in something.

急に熱が冷めてしまった。

Common

"熱い眼差し"

— A passionate look/stare.

熱い眼差しを向ける。

Literary

"熱血"

— Hot-blooded; passionate.

熱血教師。

Common

"微熱を帯びる"

— To have a slight feverish feeling; often used poetically for atmosphere.

夜の空気が微熱を帯びている。

Poetic

"情熱を燃やす"

— To burn with passion.

仕事に情熱を燃やす。

Formal

Easily Confused

発熱する vs 熱中症 (Netchusho)

Both involve heat and sickness.

Netchusho is heatstroke (external heat); Hatsunetsu is a fever (internal response).

夏は熱中症に注意。風邪で発熱する。

発熱する vs 微熱 (Binetsu)

Both are types of fevers.

Binetsu is specifically a slight fever; Hatsunetsu is the general verb for any fever.

発熱したが、まだ微熱だ。

発熱する vs 発光 (Hakko)

Both start with 'Hatsu'.

Hakko is emitting light; Hatsunetsu is emitting heat.

ホタルが発光する。病気で発熱する。

発熱する vs 平熱 (Heinetsu)

Both contain 'Netsu'.

Heinetsu is normal temperature; Hatsunetsu is having a fever.

平熱は36度だが、今は発熱している。

発熱する vs 興奮 (Kofun)

Both can mean getting 'heated'.

Kofun is emotional excitement; Hatsunetsu is physical fever.

試合で興奮する。風邪で発熱する。

Sentence Patterns

Netsu ga arimasu.

熱があります。

Hatsunetsu shimashita.

発熱しました。

Hatsunetsu shite iru node, ...

発熱しているので、休みます。

Hatsunetsu shita baai wa, ...

発熱した場合は、来ないでください。

Hatsunetsu o tomonau ...

発熱を伴う咳がひどい。

Hatsunetsu ga tsuzuku.

発熱が三日続いている。

Hatsunetsu no kijo.

発熱の機序を説明する。

Kyugeki na hatsunetsu.

急激な発熱により容体が悪化した。

Word Family

Nouns

発熱 (Fever/Heat generation)

発熱者 (Person with fever)

発熱外来 (Fever clinic)

Verbs

発熱する (To have a fever)

熱する (To heat up)

熱を出す (To get a fever)

Adjectives

熱い (Hot to touch)

暑い (Hot weather)

熱烈な (Passionate)

体温 (Body temperature)

風邪 (Cold)

インフルエンザ (Flu)

解熱剤 (Fever reducer)

検温 (Measuring temperature)

How to Use It

frequency

Very high in medical, news, and official contexts; moderate in daily life.

Common Mistakes

Using 'Hatsunetsu' for weather. → Atsui (暑い).
Hatsunetsu is for body or object heat generation, not ambient temperature.
Saying 'Netsu o hatsunetsu suru'. → Hatsunetsu suru.
It's redundant to include 'netsu' twice.
Confusing 'Hatsunetsu' and 'Hatsumei'. → Hatsunetsu (fever), Hatsumei (invention).
Watch the second kanji closely.
Using 'Hatsunetsu' for anger. → Atama ni kuru / Okoru.
Hatsunetsu is only for physical temperature.
Treating it as a Class 1 verb (hatsunetsu-u). → Hatsunetsu-suru.
It is always a suru-verb.

Tips

Using 'Te-iru'

Always use 'hatsunetsu shite iru' to describe the ongoing state of having a fever. 'Hatsunetsu shita' means the fever started.

Kango vs Wago

Hatsunetsu is Kango (Chinese origin). Use it to sound more precise, like saying 'manifesting a fever' instead of 'getting a fever'.

Absence Notes

In Japan, always mention the specific temperature if you are reporting 'hatsunetsu' to your boss.

The 'Hatsu' Kanji

The kanji 発 is used in many 'starting' words like 'shuppatsu' (departure). Think of the fever 'departing' from your normal state.

Medical Forms

When you see '発熱' on a form, look for a checkbox for 'ari' (yes) or 'nashi' (no).

The 'N' sound

Ensure the 'n' in 'netsu' is clear. Don't let it get swallowed by the 'tsu' before it.

Stroke Order

The bottom of 熱 is four dots (fire). Make sure to write them from left to right.

Clinic Visits

In Japan, you must call ahead if you are 'hatsunetsu shite iru' before visiting a clinic.

Exothermic

Remember 'hatsunetsu-hanno' for chemistry class to mean heat-releasing reactions.

Ancient Roots

The kanji for 'Hatsu' originally depicted feet stepping out, symbolizing something emerging.

Memorize It

Mnemonic

Think of a 'HAT' (Hatsu) that is 'HOT' (Netsu). When you wear a hot hat, you get a fever!

Visual Association

Imagine a thermometer coming out of a person's head like a rocket 'launching' (Hatsu) heat (Netsu).

Word Web

Sickness Temperature Hospital Thermometer Bed Sweat Medicine Chills

Challenge

Try to use 'hatsunetsu' in a sentence explaining why you missed a fake meeting today.

Word Origin

Sino-Japanese (Kango). '発' (Hatsu) comes from Middle Chinese /pʉat/ meaning 'to send out' or 'to happen.' '熱' (Netsu) comes from Middle Chinese /ɲiet/ meaning 'heat.'

Original meaning: To generate heat or to have heat emerge.

Japonic (Sino-Japanese vocabulary).

Cultural Context

Be careful when asking someone if they are 'hatsunetsu-shite-iru' as it can imply they are 'contagious' and should leave.

In the West, 'running a fever' is the common idiom. We focus on the 'running' (continuation), whereas Japanese 'hatsunetsu' focuses on the 'generation' of heat.

Used in countless medical dramas like 'Doctor-X'. Commonly found in news headlines during flu outbreaks. Appears in manuals for 'Hiepita' and 'Pocari Sweat'.

Practice in Real Life

Real-World Contexts

At a Clinic

いつから発熱しましたか？
最高で何度まで上がりましたか？
発熱以外に症状はありますか？
解熱剤は飲みましたか？

At School/Work

発熱のため休みます。
発熱したので早退します。
発熱がある生徒がいます。
発熱の報告をします。

Reading News

発熱者が増加している。
発熱外来が混雑している。
発熱を伴う新型ウイルス。
発熱の初期症状。

Pharmacy

発熱に効く薬はありますか？
発熱を抑える薬です。
子供の発熱用です。
発熱が続く場合に。

Science Lab

この反応は発熱します。
発熱量を計算する。
発熱反応の実験。
容器が発熱している。

Conversation Starters

"最近、周りで発熱している人はいますか？ (Are there people with fevers around you lately?)"

"発熱した時、一番辛いことは何ですか？ (What is the hardest part for you when you have a fever?)"

"子供が発熱したら、どう対処しますか？ (How do you handle it if your child gets a fever?)"

"ワクチンで発熱したことはありますか？ (Have you ever had a fever from a vaccine?)"

"発熱に一番効く食べ物は何だと思いますか？ (What food do you think works best for a fever?)"

Journal Prompts

最後に発熱した時のことを詳しく書いてください。 (Write in detail about the last time you had a fever.)

日本の「発熱外来」についてどう思いますか？ (What do you think about Japan's 'fever clinics'?)

発熱した時に食べたい料理とその理由。 (The dish you want to eat when you have a fever and why.)

学校や会社での発熱時のルールについて。 (About rules regarding fevers at school or work.)

「知恵熱」という言葉について調べた感想。 (Your thoughts after researching the word 'Chienetsu'.)

Frequently Asked Questions

10 questions

In formal writing and medical settings, yes. In casual speech, no. 'Netsu ga deru' is the standard for talking to friends.

It's better to say 'Hatsunetsu shite imasu' (I am running a fever) or 'Hatsunetsu ga arimasu' (I have a fever).

Usually 37.5°C (99.5°F) is the official threshold for schools and workplaces.

No, it can apply to animals and even chemical reactions (exothermic reactions).

You can say 'Netsu ga sagatta' or 'Genetsu shimashita'.

It is a specialized 'fever clinic' established during the pandemic to treat people with potential infections.

No, 'Hatsunetsu' is strictly clinical. Use 'Jounetsu' or 'Netchu' for passion.

It is a Class 3 (Irregular/Suru) verb.

It has 'fire' (火) at the bottom, which helps you remember it means heat.

Yes, 'Hatsunetsu' can be used for machines or batteries generating heat.