Why does fog look white?
The reason is the same as why clouds are white.Fog looks white because the tiny water droplets drifting in the air scatter sunlight the same way, no matter what color the light is. Red, green, and blue are all scattered about equally and reach our eyes, so they mix and look white. Fog is "a cloud at ground level," so it is white for the same reason clouds are.
Fog is made of tiny water droplets
Fog forms when water vapor in the air (water as an invisible gas) cools down and turns into tiny floating water droplets. The UK's Met Office describes fog as "a cloud at ground level." According to the Royal Meteorological Society in the UK, fog droplets are about 0.01–0.1mm across on average, so each one is too small to see.
Droplets scatter every color equally
Sunlight is a mix of many colors of light, such as red, green, and blue. Very tiny particles like air molecules scatter blue light strongly, which is why a clear sky looks blue. Fog and cloud droplets, on the other hand, are about as large as the length of light waves, so they scatter every color of light almost equally. The Japan Meteorological Agency also explains that fog and mist look white because tiny water droplets scatter sunlight regardless of wavelength (the difference in light's color).
All colors mixed together make white
When light of every color reaches our eyes in the same proportions, we see it as white. Inside fog, countless droplets scatter light in all directions, so the fog itself looks white and bright, while the scenery beyond it becomes blurry and hard to see.
Sometimes it looks a different color
Still, fog does not always look pure white. According to the US National Oceanic and Atmospheric Administration (NOAA), clouds look gray when they become thick and light has trouble passing through, and they take on the color of the light that reaches them at sunrise or sunset. Fog, made of the same water droplets, is also thought to change its shade depending on how light falls on it.
Want to know more?
- Under international rules, it is called "fog" when you can see less than 1 km ahead, and "mist" when you can see farther than that.
- Fog droplets form around tiny cores such as dust in the air or grains of sea salt. Fog is said to become thicker more easily in industrial areas and over the sea, where there are many of these particles.
- According to the UK's Met Office, thick fog that cuts how far you can see to under 100 m can greatly affect traffic.
Quick quiz: test yourself
Why does fog look white?
Show the answer
- Droplets scatter all colors equally
- Droplets scatter only blue light
- Dust in the air is white
Droplets scatter all colors equally The tiny water droplets in fog scatter red, green and blue light about equally. All the colors reach our eyes mixed together, so fog looks white.
The tiny water droplets in fog scatter red, green and blue light about equally. All the colors reach our eyes mixed together, so fog looks white.
Next quiz ›Sources
- 雲・大気現象・大気光象について気象庁 (in Japanese)
- The Color of CloudsNational Oceanic and Atmospheric Administration (NOAA)
- What is fog?Met Office
- I tried to catch the fog... but I "mist"!Royal Meteorological Society
This article was written after checking the sources above as of 2026-10-03. Explanations may change as research progresses. Photo credits are shown below each photo.
