Translation guide
The English verb 'redden' can mean to become red (intransitive) or to make something red (transitive). In Japanese, these are expressed with different verbs. The most common and natural way is to use 赤くなる (intransitive) or 赤くする (transitive). There are also specific verbs for blushing, ripening, or reddening due to inflammation.
To turn red or become red in color, often due to natural processes, emotions, or physical changes.
The most common and neutral way to say 'become red'. Used for leaves, sky, face, etc.
In autumn, the leaves turn red.
I was embarrassed and my face turned red.
Often used for cheeks, sky, or fruit becoming red. Slightly literary or poetic.
Her cheeks reddened.
Specifically for skin flushing or blushing, often due to emotion or health. Formal/medical.
My face flushed with nervousness.
To cause something to become red, such as dyeing, painting, or applying color.
Specifically when a person's face becomes red due to embarrassment, shame, or shyness.
When fruits or vegetables become red as they ripen.
When eyes or skin become red due to irritation, crying, or inflammation.
赤くなる is the most general and can be used for anything turning red. 赤らむ is often used for cheeks, sky, or fruit and has a slightly poetic nuance. 紅潮する is specifically for skin flushing and is more formal/medical.
There is no single Japanese verb that covers all uses of 'redden'. Always choose the expression based on whether it's intransitive or transitive, and what is becoming red.
She reddened her cheeks.
He blushed and looked down.
リンゴが色づいてきた。
The apples are starting to redden.