1To become red; to redden — used for things or faces taking on a reddish color (e.g., blushing or reddening from cold).
寒さで彼女の頬が赤らんでいた。
Her cheeks were reddened from the cold.
恥ずかしくて顔が赤らんだ。
I blushed from embarrassment.
夕陽で西の空が赤らんでいる。
The western sky is reddening from the sunset.