Headlight foging issue

[Benny771]

Hi:
What is the cause of this?
Is there a breather tube that needs cleaning or is the seal most likely gone.

How easy is this to repair. Photo would be nice.

[A930Rocket]

Not sure what causes it, but you can clean the inside of the lens housing by removing the light fixture from the fender, remove the bulb and then use a cloth secured to a thin piece of wood with rubbing alcohol on it inserted in the lightbulb socket to clean the backside of the glass.

[billjam]

I have this problem because I replaced the LHD lenses with RHD lenses without using a new rubber ring between the lens and the reflector.
Water gets in sometimes in the rain or when I wash the car and it fogs up the inside. They always seem to dry out after a few days.
Been meaning to get new seals but I always forget to add them to my shopping cart when I'm buying stuff from PP.

[Benny771]

Forgot to say ,

H5 lights is what i have. Is there not a breather on these lens casings?

[JFairman]

I've cleared the fog from the inside of the lenses on H5's by removing them, then removing the bulbs and filling them halfway with dishwashing soap and hot water and shaking them real good for a minute. Then rinse them out several times with clean water to get the soap out.

Then I poured in some isopropyl alcohol and shook them to slosh it around for about a minute again.

After that I blew them out with oil free compressed air and then set them in the sun for a couple hours to dry them out completely.

After all that they were crystal clear again.

I think the fog is actually a mildew or fungus that grows on glass surfaces in humid air after some time.
The same thing or something very similar happens on the inside surface of mounted glass filters on camera lenses and on the inner elements of some camera lenses too.