Meaning & use
fog up
Last updated
Meanings
verbintransitive
To become covered with a thin layer of mist so you cannot see through clearly.
Grammar: No object; the thing that gets misty is the subject: My glasses fogged up.
Patterns
- something fogs up
- something fogs up in the cold
- something fogs up when you breathe on it
My glasses fog up every time I come in from the cold.
The car windows fogged up within minutes in the rain.
Her goggles fog up when she swims without spitting in them.
verbtransitive
To make a surface, especially glass, become covered with mist.
Grammar: Takes an object, which usually comes between 'fog' and 'up': The steam fogged the mirror up.
Patterns
- fog something up
- fog up something
- something fogs something up
The hot shower fogged the bathroom mirror up.
Don't breathe on the lens — you'll fog it up.
The steam from the kettle fogged up the kitchen window.
verbtransitivefigurative
To make someone confused or unable to think clearly.
Grammar: Takes a person as object; usually in the passive: My mind was fogged up by tiredness.
Patterns
- fog someone up
- be fogged up by something
Lack of sleep had fogged his mind up completely.
The complicated instructions fogged me up, and I made a silly mistake.
Word forms
| third person singular | fogs up |
|---|---|
| past tense | fogged up |
| past participle | fogged up |
| -ing form | fogging up |
Common combinations
- fog up the mirror
- A hot shower will fog up the mirror in seconds.
- glasses fog up
- My glasses fog up as soon as I wear a mask.
- windows fog up
- The windows fog up when it's cold outside and warm inside.
- goggles fog up
- Skiers often complain that their goggles fog up.
- fog up completely
- The windshield fogged up completely before I turned on the defroster.
Synonyms and how they differ
- mist up
- Very close in meaning, but 'mist up' is more common in British English and often suggests a lighter, finer film of moisture.
- steam up
- Use this when heat or steam is the cause; 'fog up' is broader and can also describe cold condensation.
- cloud
- Used mainly in the phrase 'cloud over' for glass or eyes; it is more literary and less common in everyday speech.
Opposites
Word family
Commonly confused: fog up or frog? fog up or fogged?
fog up vs frog
A common spelling mistake: 'frog' is the animal, while 'fog' is the mist that covers glass.
fog up vs fogged
This is the past form of the verb, not a separate word; use 'fogged up' when glass has mist on it.
Practice
Which sentence uses 'fog up' correctly?
Choose one answer.
'Fog up' means glass becomes misty, so glasses fogging up from hot coffee is correct. Option 2 wrongly treats 'fog up' as if it meant 'put on'; option 3 uses 'to' where no preposition is needed; option 4 makes no sense because fogging up is not a social activity.
Make it your own
Write a sentence using “fog up”, then check it and compare it with the examples above.