Translation guide
How to say 'become dirty' in Japanese depends on what is getting dirty and how. The most common way is to use the adjective 汚い (kitanai, 'dirty') with the verb なる (naru, 'to become'). There are also specific verbs for soiling, staining, or tarnishing.
To say that something becomes unclean or covered in dirt/grime.
My hands got dirty, so I'll wash them.
An intransitive verb meaning 'to become dirty/soiled'. Often implies a more noticeable stain or soiling, and can be used for clothes, surfaces, or reputation.
白いシャツがすぐ汚れる。
White shirts get dirty quickly.
床が汚れている。
The floor is dirty.
Same kanji but different reading. This is the transitive version 'to make dirty', but can be used in passive form 汚される to mean 'become dirty (by someone/something)'. Less common for simple state change.
This reading is often spiritual or metaphorical (defilement), not physical dirt.
心が汚れる。
One's heart becomes defiled.
To say that something gets a stain or spot from a specific substance.
Literally 'a stain attaches'. Used when a stain appears on fabric, paper, etc. Often with the substance marked by で.
コーヒーでシャツに染みがついた。
My shirt got a coffee stain.
Intransitive verb meaning 'to be stained'. Often used when a stain soaks in and becomes hard to remove.
インクが布に染みた。
The ink stained the cloth.
To say that something becomes impure or harmful due to pollution.
Passive form of 汚染する (to pollute/contaminate). Used for environmental pollution, radiation, etc.
川が工場排水で汚染された。
The river was polluted by factory wastewater.
Can also be used for environmental dirt, but less formal than 汚染される.
海が油で汚れた。
The sea became dirty with oil.
To say that something loses its luster or becomes dull.
Means 'to become cloudy/dim/tarnished'. Used for mirrors, glass, metal surfaces losing shine.
銀のスプーンが曇った。
The silver spoon became tarnished.
Means 'to become dull/sober/lose brightness'. Used for colors, metals, or even mood.
To say that someone accidentally dirties their clothes or body with excrement.
Literally 'to leak/let out'. Used for urinary or fecal incontinence. Often used in past tense 漏らした or 漏らしてしまった.
子供がパンツを漏らした。
The child soiled his pants.
A euphemistic phrase meaning 'to have an accident' (especially toilet-related). More polite than 漏らす.
お年寄りが粗相をしてしまった。
The elderly person had an accident.
汚くなる (kitanaku naru) is a general state change and can be used for anything becoming dirty. 汚れる (yogoreru) often implies a more noticeable soiling or staining, and is commonly used for clothes and surfaces. 汚くなる is more colloquial and flexible.
You cannot say 汚いなる. The adjective must be turned into an adverb: 汚くなる.
The gold ring became dull.