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.
The child is acting up and it's a problem.
Specifically means throwing a tantrum or being stubborn, often used for young children.
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.
Stop acting up during class.
Means to rebel or defy, suitable when the acting up is a form of rebellion, especially in teenagers.
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.
My computer is acting up and freezes often.
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.
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.
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.
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.
Means 'to worsen' or 'aggravate', suitable when a condition becomes more severe.
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.
My cold seems to be acting up again.