Translation guide
The English phrase "act up" has several distinct meanings, from misbehaving to malfunctioning. This guide breaks down the most common uses and provides natural Japanese equivalents.
To behave badly or disobediently, often used for children or people acting out.
Literally 'to say selfish things', this is a common way to describe a child acting up or being demanding.
子供がわがままを言って困っている。
The child is acting up and it's a problem.
Specifically means throwing a tantrum or being stubborn, often used for young children.
息子がおもちゃを買ってほしくて駄々をこねた。
My son acted up because he wanted me to buy him a toy.
Means to mess around or fool around, often in a disruptive way. Can be used for older children or even adults acting up.
授業中にふざけるのはやめなさい。
Stop acting up during class.
Means to rebel or defy, suitable when the acting up is a form of rebellion, especially in teenagers.
思春期の子供は親に反抗することがある。
Adolescent children sometimes act up against their parents.
To fail to work properly, often intermittently or annoyingly.
A general phrase meaning 'in bad condition', used for machines, body parts, or even abstract things.
パソコンの調子が悪くて、よくフリーズする。
My computer is acting up and freezes often.
膝の調子が悪いので、走れない。
My knee is acting up, so I can't run.
Means 'to break down' or 'malfunction', more definitive than 調子が悪い. Use when something clearly stops working.
エアコンが故障して、冷たい風が出ない。
The air conditioner is acting up and not blowing cold air.
Similar to 調子が悪い but often used for body parts or health. Can also be used for machines.
昨日から胃の具合が悪い。
My stomach has been acting up since yesterday.
To flare up or become problematic again, often used for medical conditions or recurring issues.
Means 'to recur' or 'relapse', used for illnesses or problems that come back.
古傷が再発して痛む。
My old injury is acting up and hurts.
Means 'to return' or 'come back', often used for symptoms or bad weather. More colloquial than 再発する.
風邪がぶり返したみたいだ。
My cold seems to be acting up again.
Means 'to worsen' or 'aggravate', suitable when a condition becomes more severe.
ストレスで症状が悪化した。
The symptoms acted up due to stress.
Do not translate "act up" literally as 行動する上 or similar. It will not be understood. Use the context-appropriate phrases above.