反応 in 30 Seconds
- Hannou means 'reaction' or 'response' in Japanese, covering everything from human emotions to chemical changes and mechanical inputs.
- It is commonly used as a Suru-verb (反応する) with the particle 'ni' to indicate the cause of the reaction.
- Unlike 'henji' (a verbal reply), 'hannou' is often involuntary or an objective observation of an effect.
- It is essential for science, social media engagement, medical side effects, and describing interpersonal dynamics in daily life.
The Japanese word 反応 (はんのう - hannou) is a fundamental noun that encompasses the broad concept of 'reaction' or 'response.' In its most basic form, it describes the way a person, animal, or even an inanimate object behaves or changes in direct response to a specific stimulus, action, or statement. It is composed of two kanji: 反 (han), meaning 'anti-' or 'counter-', and 応 (nou/ou), meaning 'respond' or 'apply.' Together, they literally suggest a 'counter-response' to an external force.
- Interpersonal Context
- When you tell a joke and someone laughs, their laughter is the 'hannou'. If you ask a question and someone ignores you, that lack of response is also a 'hannou'.
- Scientific Context
- In chemistry, it refers to the process where substances interact to form new ones (化学反応 - kagaku hannou). In biology, it refers to a physiological response to a stimulus, like a pupil dilating in the dark.
- Digital Context
- In the age of social media, 'hannou' is often used to describe engagement—likes, comments, and shares are all forms of user reaction.
彼にプレゼントをあげたが、あまり反応がなかった。
Understanding 'hannou' requires recognizing that it is more passive than 'henji' (a verbal reply). While 'henji' is a conscious answer to a question, 'hannou' can be involuntary, such as a reflex or an emotional state. It is the visible or measurable effect of a cause. For instance, a market's 'hannou' to economic news isn't a spoken word, but a change in stock prices.
薬の反応を見るために、しばらく待ちましょう。
- Physical Reaction
- Refers to reflexes or bodily changes, such as an allergic reaction (アレルギー反応).
- Mechanical Reaction
- How a machine or software responds to input, like a touch screen's responsiveness.
In summary, 'hannou' is the universal term for 'A leads to B'. Whether it is a child's face lighting up at a toy, a chemical turning blue in a test tube, or a computer freezing after a command, all these instances are categorized as 'hannou'. It is a neutral term that can be modified by adjectives like 'ii' (good), 'warui' (bad), 'usui' (thin/weak), or 'surudoi' (sharp/quick) to provide more detail about the nature of the response.
Using 反応 (hannou) correctly involves understanding its grammatical versatility. As a noun, it functions as the subject or object of a sentence. As a Suru-verb (反応する), it describes the act of reacting. It is most commonly paired with the particle に (ni) to indicate what is being reacted to.
- Structure: [Stimulus] + に + 反応する
- Example: 光に反応する (React to light). This is the standard way to show the cause of the reaction.
- Structure: [Adjective] + 反応
- Example: 素早い反応 (Quick reaction). Common adjectives include 'nibui' (slow/dull) and 'bikkyuri' (surprised).
私の冗談に、彼女は全く反応しなかった。
In professional settings, 'hannou' is used to gauge customer feedback or market trends. A 'hannou ga ii' (good reaction) product is one that is selling well or receiving praise. In a medical context, doctors look for 'hannou' in neurological tests or allergy screenings. It is important to note that 'hannou' is generally objective. It describes the fact that a change occurred, rather than the emotional intent behind it.
このボタンは、強く押さないと反応しません。
When discussing social media, 'hannou' is the go-to word for engagement. If you post a photo and get many likes, you would say 'hannou ga ookii' (the reaction is big). This usage is very common among younger generations and digital marketers. In more formal writing, 'hannou' can be replaced by 'ouda' (response) or 'tekitou' (appropriate response), but 'hannou' remains the most flexible and widely understood term across all levels of formality.
You will encounter 反応 (hannou) in a vast array of daily situations in Japan. From the classroom to the laboratory, and from the office to the living room, it is a ubiquitous term. In schools, science teachers use it constantly when discussing experiments. In offices, managers use it to discuss how clients felt about a proposal.
- Daily Conversation
- 'Aitsu, hannou ga usui ne' (That guy's reaction is weak/He's not very responsive).
- News and Media
- Reporting on public outcry or support for a new law: 'Kokumin no hannou' (The citizens' reaction).
- Medical/Health
- Discussing side effects: 'Fukuhannou' (Side reaction/Side effect, specifically for vaccines).
ワクチンの副反応で熱が出ました。
In the entertainment industry, variety shows often focus on 'reaction' (often called 'リアクション' - riakushon, but described as 'hannou'). Comedians are praised for their 'hannou' to spicy food or scary pranks. On YouTube, 'reaction videos' are called 'hannou douga'. This shows how the word bridges the gap between technical terminology and pop culture.
新商品の市場の反応を調査する。
In sports, commentators talk about a player's 'hannou sokudo' (reaction speed). A goalkeeper making a save or a batter hitting a fast pitch are classic examples of 'hannou'. In essence, anywhere there is an action followed by a result, you will hear this word. It is one of the most useful words for describing the dynamics of the world around you.
While 反応 (hannou) is versatile, learners often confuse it with other 'response' words. The most common mistake is using 'hannou' when 'henji' (reply) is required. 'Henji' is specifically for answering a call or a letter. You wouldn't say 'I wrote a hannou to his email'—that would sound like you had a physical reaction to the email, not that you replied to it.
- Hannou vs. Henji
- Hannou: Involuntary or broad response. Henji: Direct verbal/written answer.
- Hannou vs. Taiou
- Taiou means 'handling' or 'dealing with' a situation. If a customer complains, your 'taiou' is how you fix it; their 'hannou' is how they feel about your fix.
× メールの反応を待っています。
○ メールの返事を待っています。
Another mistake is using 'hannou' for 'kansou' (impression/opinion). If someone asks for your 'hannou' on a movie, they are asking how you physically or emotionally reacted in the moment. If they want your considered opinion, they should ask for your 'kansou'. 'Hannou' is more immediate and raw.
× 彼の意見に反応です。
○ 彼の意見に反対です。
Lastly, be careful with the particle. It is almost always 'Stimulus + に + 反収'. Using 'o' (object particle) is rare unless you are 'showing' a reaction (反応を示す). Forgetting the 'ni' can make the sentence sound disjointed. Remember: you react *to* something, so 'ni' is your best friend here.
Japanese has several words that overlap with 反応 (hannou). Choosing the right one depends on the level of formality and the specific type of response you are describing. Here are the most common synonyms and related terms.
- 応答 (Outou)
- A more formal word for 'response' or 'answer,' often used in technical or radio communications (e.g., 'No response from the satellite').
- 対応 (Taiou)
- Focuses on the action taken to address a stimulus. It means 'correspondence' or 'handling'.
- レスポンス (Responsu)
- The katakana version of 'response'. Used frequently in business and IT to describe how quickly someone gets back to you or how fast a server responds.
緊急時の対応を訓練する。
There is also 反響 (hankyou), which means 'echo' or 'reverberation'. It is used metaphorically to describe a huge public sensation or 'buzz' around a topic. While 'hannou' is a single reaction, 'hankyou' implies a widespread, echoing effect throughout society.
そのニュースは大きな反響を呼んだ。
Finally, 感触 (kanshoku) refers to the 'feel' or 'touch' of something, but it can be used to describe the 'vibe' or 'initial reaction' you get from a meeting. 'Hannou' is the visible result, while 'kanshoku' is the internal feeling you get about how things are going. Using these words correctly will make your Japanese sound much more natural and nuanced.
How Formal Is It?
Difficulty Rating
Grammar to Know
Particle 'ni' for targets of action.
Suru-verbs (Noun + suru).
Adverbial forms of adjectives (i -> ku, na -> ni).
Compound nouns (Noun + Noun).
Passive voice (hannou sareru - rarely used, but possible).
Examples by Level
彼の反応は良かったです。
His reaction was good.
Noun + は + Adjective + です
赤ちゃんが音に反応しました。
The baby reacted to the sound.
Particle 'ni' indicates the stimulus.
反応がありません。
There is no reaction.
Noun + が + ありません
いい反応ですね！
That's a good reaction!
Adjective + Noun
猫が光に反応する。
The cat reacts to light.
Suru-verb 'hannou suru'
彼の反応は面白いです。
His reaction is funny.
Noun + は + Adjective
だれも反応しませんでした。
No one reacted.
Negative past tense of 'hannou suru'
ボタンを押しても反応がない。
Even if I press the button, there is no reaction.
Te-form + mo (even if)
プレゼントにどんな反応をしましたか？
How did they react to the present?
Danna + Noun + o + shimashita ka
冷たい水に反応して、体が震えた。
Reacting to the cold water, my body shook.
Te-form for cause and effect.
先生の質問に素早く反応した。
I reacted quickly to the teacher's question.
Adverbial use of 'subayaku'.
薬を飲んだが、反応がなかった。
I took the medicine, but there was no reaction.
Conjunction 'ga' (but).
彼女は私の話に薄い反応を見せた。
She showed a weak reaction to my story.
Hannou o miseru (to show a reaction).
この機械は声に反応します。
This machine reacts to voices.
Noun + ni + hannou suru.
犬は飼い主の声にすぐ反応する。
Dogs react immediately to their owner's voice.
Adverb 'sugu' (immediately).
みんなの反応が気になります。
I'm curious about everyone's reaction.
Ki ni naru (to be curious/worried).
SNSでの反応が予想以上に大きかった。
The reaction on social media was bigger than expected.
Yosou ijou (more than expected).
化学反応の実験を理科室で行う。
We conduct chemical reaction experiments in the science lab.
Compound noun: Kagaku hannou.
アレルギー反応が出たので、病院へ行った。
I had an allergic reaction, so I went to the hospital.
Hannou ga deru (reaction appears).
市場の反応を見て、価格を決めます。
We will decide the price after seeing the market's reaction.
Te-form + mite (after seeing).
彼は批判に対して過剰に反応した。
He reacted excessively to the criticism.
Kajou ni (excessively).
このセンサーは熱に敏感に反応する。
This sensor reacts sensitively to heat.
Binkan ni (sensitively).
観客の反応は非常にポジティブだった。
The audience's reaction was very positive.
Adverb 'hijou ni' (extremely).
彼の言葉に、彼女は複雑な反応を示した。
She showed a complex reaction to his words.
Fukuzatsu na (complex).
政府の新しい政策に対する国民の反応は冷ややかだ。
The public reaction to the government's new policy is cold.
Tai suru (towards/against).
ワクチンの副反応で腕が痛むことがある。
The side reaction of the vaccine can cause arm pain.
Compound noun: Fukuhannou.
そのニュースは世界中で大きな反響と反応を呼んだ。
That news caused a huge sensation and reaction worldwide.
Hannou o yobu (to cause/invite a reaction).
彼はわざと無反応を装った。
He intentionally pretended to be unresponsive.
Muhannou (no reaction) + o yosou (pretend).
瞳孔が光に反応する速度を測定する。
Measure the speed at which the pupil reacts to light.
Noun + ni + hannou suru + sokudo.
投資家たちは大統領の発言に即座に反応した。
Investors reacted immediately to the President's remarks.
Sokuza ni (immediately/on the spot).
彼の脳は特定の刺激に強く反応している。
His brain is reacting strongly to specific stimuli.
Te-iru (continuous state).
この物質は水と混ぜると激しい反応を起こす。
This substance causes a violent reaction when mixed with water.
Hannou o okosu (to cause a reaction).
その外交問題に対する各国の反応は様々である。
The reactions of various countries to that diplomatic issue vary.
Samazama de aru (are varied).
心理学的に見て、それは防御反応の一種だと言える。
From a psychological perspective, it can be said to be a type of defense mechanism (reaction).
Bougyo hannou (defense reaction).
彼の無意識の反応が、本心を物語っていた。
His subconscious reaction told his true feelings.
Muishiki no (subconscious).
市場の過剰反応を抑えるための措置を講じる。
Take measures to suppress the market's overreaction.
Kajou hannou (overreaction).
その実験結果は、理論通りの反応を示さなかった。
The experimental results did not show the reaction as theorized.
Riron-doori (according to theory).
彼女の鋭い反応のおかげで、事故は未然に防がれた。
Thanks to her sharp reaction, the accident was prevented.
Mizen ni fusegu (prevent beforehand).
この現象は、連鎖反応的に社会全体に広がった。
This phenomenon spread through society like a chain reaction.
Rensa hannou-teki ni (like a chain reaction).
聴衆の微妙な反応の変化を読み取ることが重要だ。
It is important to read the subtle changes in the audience's reaction.
Bimyou na (subtle).
生体内の複雑な代謝反応を網羅的に解析する。
Comprehensively analyze the complex metabolic reactions within a living organism.
Moura-teki ni (comprehensively).
その哲学的問いに対し、彼は沈黙という反応を選んだ。
To that philosophical question, he chose the reaction of silence.
Chinmoku to iu hannou (the reaction called silence).
核分裂反応の制御は、現代科学の至上命題の一つである。
The control of nuclear fission reactions is one of the ultimate mandates of modern science.
Kakubunretsu hannou (nuclear fission reaction).
彼の言動は、周囲の期待に対する一種の拒絶反応だった。
His words and actions were a kind of rejection reaction to the expectations around him.
Kyozetsu hannou (rejection reaction/allergic rejection).
その政策転換が引き起こす二次的な反応を予測するのは困難だ。
It is difficult to predict the secondary reactions caused by that policy shift.
Niji-teki na (secondary).
抗原抗体反応を利用した検査キットが普及している。
Test kits utilizing antigen-antibody reactions are widespread.
Kougen koutai hannou (antigen-antibody reaction).
彼の冷徹な反応は、長年の経験からくる自己防衛本能だろう。
His cold reaction is likely a self-defense instinct stemming from years of experience.
Reitetsu na (cold/composed).
社会構造の変革に伴い、人々の価値観に劇的な反応が見られた。
With the transformation of social structures, a dramatic reaction was seen in people's values.
Ni tomonai (accompanying).
Common Collocations
Common Phrases
Often Confused With
Henji is a verbal or written reply. Hannou is a general reaction.
Taiou is how you handle a situation. Hannou is the result or response.
Kansou is a thought or impression. Hannou is an immediate reaction.
Idioms & Expressions
Easily Confused
Sentence Patterns
How to Use It
Generally neutral, but can be negative if you say 'hannou ga usui'.
Always use 'ni' with 'hannou suru'.
The word is equally common in both fields.
Tips
Use with 'ni'
Always remember that the thing you are reacting to is marked with 'ni'. This is the most important grammar rule for this word. For example, 'hikari ni hannou suru' (react to light). It makes your Japanese sound natural.
Hannou vs Henji
Don't use 'hannou' for 'reply'. 'Henji' is for words, 'hannou' is for actions or states. If you wait for an email, wait for a 'henji'. If you wait for a smile, wait for a 'hannou'.
Aizuchi is Hannou
In Japan, giving a 'hannou' while listening is vital. Use words like 'un', 'sou desu ne', and 'heee'. This shows you are engaged. A lack of 'hannou' can be interpreted as a lack of interest.
Kagaku Hannou
This is the term for chemical reactions. You will see it in every science context. It's also used metaphorically for good teamwork. 'Kagaku hannou o tanoshimu' means to enjoy the synergy.
Fukuhannou
This specifically means 'side effect' for vaccines. For other medicines, 'fukusayou' is more common. Knowing this distinction is helpful for health-related conversations. It's a very common word in recent news.
Social Media
Likes and comments are 'hannou'. If you want more engagement, you want more 'hannou'. 'Hannou ga ooi' means your post is popular. It's a key word for digital marketing.
Common Adjectives
Pair 'hannou' with 'ii' (good), 'warui' (bad), 'hayai' (fast), or 'nibui' (slow). These are the most frequent pairings. They help you describe the quality of the response clearly.
Kyozetsu Hannou
This means 'rejection reaction'. It's used for organ transplants but also for hating something. 'Sono kangae ni wa kyozetsu hannou o okosu' means 'I'm repulsed by that idea'. It's a strong expression.
Listen for 'ga'
In conversation, you'll often hear 'hannou ga nai' (no reaction). This is a common way to express frustration. Pay attention to how people use it when they are ignored. It's a key phrase for understanding social dynamics.
Formal Writing
In essays, use 'hannou o shimesu' (to show a reaction). It sounds more academic and professional than 'hannou suru'. This is great for JLPT N2/N1 level writing. It adds a level of sophistication.
Memorize It
Word Origin
Sino-Japanese (Kango)
Cultural Context
The importance of verbal/non-verbal reaction in conversation.
The 'Reaction King' (リアクション芸人) trope.
The rise of 'Hannou-shuu' (reaction compilations) on Japanese YouTube.
Practice in Real Life
Real-World Contexts
Conversation Starters
"そのニュースを聞いて、どんな反応をしましたか？ (How did you react when you heard that news?)"
"最近、SNSで反応が良かった投稿はありますか？ (Have you had any posts with good reactions on social media lately?)"
"彼は冗談に対してどんな反応をしますか？ (How does he react to jokes?)"
"新しいデザインについて、みんなの反応はどう？ (What's everyone's reaction to the new design?)"
"この薬、何か変な反応はありましたか？ (Did you have any strange reactions to this medicine?)"
Journal Prompts
今日、一番驚いた反応は何でしたか？ (What was the most surprising reaction you saw today?)
自分が他人の言葉に過剰に反応してしまったことはありますか？ (Have you ever overreacted to someone's words?)
理想的な『いい反応』とはどんなものだと思いますか？ (What do you think is an ideal 'good reaction'?)
SNSの反応を気にしすぎてしまうことはありますか？ (Do you ever worry too much about social media reactions?)
化学反応のように、誰かと出会って自分が変わった経験はありますか？ (Have you ever had an experience where meeting someone changed you, like a chemical reaction?)
Frequently Asked Questions
10 questionsYes, 'arerugii hannou' is the standard term for an allergic reaction. It describes the body's immune system responding to a stimulus. You can say 'hannou ga deru' if a rash appears. It is used for both minor and major medical reactions. Doctors will often ask about your 'hannou' to new medications.
No, that is a common mistake. For an email or text reply, use 'henji' (返事). 'Hannou' refers to the way you felt or acted upon reading the email, but not the act of writing back. If you say 'hannou o matsu,' it sounds like you are waiting to see how they react, not waiting for their answer. Use 'henji o matsu' instead.
Literally 'the reaction is thin.' It means someone is not giving much of a response. They might be bored, uninterested, or just a quiet person. It's often used when a joke fails or when someone is being stoic. It can be a bit of a criticism in social situations.
It is a neutral word used in both casual and formal settings. In a lab, it's a technical term. In a bar, it's a way to talk about a friend's reaction to a drink. Its level of formality changes based on the words around it, like 'desu/masu' or 'da'.
You use 'kajou ni hannou suru' (過剰に反応する). 'Kajou' means excessive. It can be used for emotional overreactions or physical ones, like an overactive immune system. It's a very common phrase in psychological and social contexts.
Yes, very much so. It describes how a machine responds to input. For example, 'Kono sumaho wa hannou ga hayai' (This smartphone has a fast reaction/is responsive). If a computer freezes, you can say 'hannou shinai' (it's not reacting/responding).
It is 'kagaku hannou' (化学反応). This is the standard term used in textbooks and laboratories. Metaphorically, it can also describe the 'chemistry' or synergy between two people. For example, 'Futari no aida ni kagaku hannou ga okita' (A chemical reaction/spark happened between the two).
'Outou' (応答) is more formal and often refers to a specific answer or a signal response. It's used in military, radio, or computer server contexts. 'Hannou' is much broader and covers any kind of change or behavior resulting from a stimulus.
Yes, it is typically categorized as N3 level on the JLPT. However, its basic meanings are useful even for beginners. By N3, you are expected to know its various uses in science, society, and grammar. It is a very high-frequency word.
Yes, but usually the 'o' is dropped to make 'hannou suru'. Adding the 'o' makes it sound like you are performing a specific, deliberate reaction. In most cases, 'ni hannou suru' is the natural choice.
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Summary
The word '反応' (hannou) is the universal Japanese term for any 'effect' caused by a 'stimulus.' Whether you are talking about a baby's smile, a chemical explosion, or a smartphone's touch screen, this is the word you need.
- Hannou means 'reaction' or 'response' in Japanese, covering everything from human emotions to chemical changes and mechanical inputs.
- It is commonly used as a Suru-verb (反応する) with the particle 'ni' to indicate the cause of the reaction.
- Unlike 'henji' (a verbal reply), 'hannou' is often involuntary or an objective observation of an effect.
- It is essential for science, social media engagement, medical side effects, and describing interpersonal dynamics in daily life.
Use with 'ni'
Always remember that the thing you are reacting to is marked with 'ni'. This is the most important grammar rule for this word. For example, 'hikari ni hannou suru' (react to light). It makes your Japanese sound natural.
Hannou vs Henji
Don't use 'hannou' for 'reply'. 'Henji' is for words, 'hannou' is for actions or states. If you wait for an email, wait for a 'henji'. If you wait for a smile, wait for a 'hannou'.
Aizuchi is Hannou
In Japan, giving a 'hannou' while listening is vital. Use words like 'un', 'sou desu ne', and 'heee'. This shows you are engaged. A lack of 'hannou' can be interpreted as a lack of interest.
Kagaku Hannou
This is the term for chemical reactions. You will see it in every science context. It's also used metaphorically for good teamwork. 'Kagaku hannou o tanoshimu' means to enjoy the synergy.
Example
化学反応が起きます。
Related Content
Related Grammar Rules
More Social words
承認
A1The act of officially accepting or approving something, such as a request, plan, or status. It is frequently used in formal or professional contexts to indicate that an authority has given the green light or acknowledged a fact as valid.
帰属
C1Kizoku refers to the state of belonging to a specific group, organization, or category, or the legal attribution of rights, property, or responsibility. It is frequently used in psychological contexts regarding identity and in legal contexts regarding ownership or jurisdiction.
意識
A1Refers to the state of being awake and aware of one's surroundings, or having a specific intention or mental focus regarding something. It can describe medical consciousness or a psychological awareness of an issue or oneself.
裏切り
A1The act of breaking trust, loyalty, or a promise made to another person or group. It often involves helping an enemy or acting against the interests of someone who relied on you.
お辞儀
A1A bow, which is the traditional Japanese gesture of bending at the waist to greet, thank, or apologize. It is a fundamental aspect of Japanese etiquette and varies in depth depending on the level of respect required.
使命
A1A significant task or duty that a person or organization feels destined or strongly obligated to fulfill. It often implies a higher purpose or a sense of calling beyond a simple everyday task.
配慮
A1配慮 (hairyo) refers to showing consideration, care, or thoughtfulness toward others' feelings, needs, or circumstances. It is frequently used in formal or polite contexts to describe acting in a way that avoids causing trouble or shows specific attention to someone's welfare.
慎重
A1The quality of being very careful and avoiding unnecessary risks. It describes a mindset or action characterized by thorough consideration and prudence before making a decision or taking a step.
争い
A1A conflict, dispute, or competition between two or more parties. It refers to a state where people disagree or fight over something, ranging from small arguments to large-scale struggles.
抗争
A1A serious struggle or conflict between opposing groups, factions, or organizations. It often implies a prolonged period of resistance, power struggles, or violent feuding.
