Translation guide
To become worse in quality, condition, or value. Japanese uses different verbs depending on what is deteriorating and whether the change is gradual or sudden.
To say that something is getting worse over time, such as health, weather, economic conditions, or quality.
The most common and versatile word for 'deteriorate' or 'worsen'. Used for health, situations, relationships, weather, etc. Can be used for both gradual and sudden worsening.
彼の病状が悪化した。
His condition deteriorated.
The weather is deteriorating.
Specifically refers to deterioration in quality, performance, or physical properties. Often used for materials, products, or abilities.
このプラスチックは日光で劣化する。
This plastic deteriorates in sunlight.
バッテリーの性能が劣化している。
The battery's performance is deteriorating.
Means 'decline' or 'drop'. Used for measurable things like ability, quality, morale, or function. Emphasizes a decrease in level.
集中力が低下している。
My concentration is deteriorating.
生活水準が低下した。
The standard of living deteriorated.
Refers to a gradual decline in strength, vitality, or power. Often used for physical or mental faculties, or the decline of nations.
体力が衰えてきた。
My physical strength is deteriorating.
その国は衰えつつある。
The country is deteriorating.
To describe something physically falling apart, rotting, or wearing out.
As above, but here emphasizes physical degradation of materials.
ゴムが劣化してひび割れた。
The rubber deteriorated and cracked.
Specifically means 'rot' or 'go bad', used for organic matter like food or wood.
果物が腐ってしまった。
The fruit deteriorated (rotted).
Means 'decay' or 'crumble', often used for wood, buildings, or remains. Has a literary or poetic nuance.
To express that morals, standards, or society are getting worse.
Means 'degenerate' or 'become decadent'. Used for moral decay, cultural decline, or corruption.
社会が退廃している。
Society is deteriorating.
Means 'fall into depravity' or 'become corrupt'. Often used for personal moral decline.
彼は堕落した生活を送っている。
He leads a deteriorated (depraved) life.
悪化する is for abstract or general worsening (health, situation). 劣化する is for concrete quality degradation (materials, performance). Use 悪化する if unsure.
While 悪くなる (わるくなる) literally means 'become bad', it can sound childish or vague. Use specific verbs like 悪化する for formal or serious contexts.
The old house is deteriorating.