front fogs misted

As above, is this something that just happens with use?, had the fog lights on for an hour or so driving at weekend, now the glass on them has misted, not completely either, its not condensation, could be the heat from the bulbs perhaps?.
Anyone elses done this?
 
More that likely the seals have gone either where the lamp plugs in at the back or where the lens meets the body. Unfortunately to check, you'll have to take the bumper off. It's worth checking soon though because otherwise mould may start to grow inside. That happened on my previous car.
 
Aren't the fogs accessible from under the bumper?, its not condensation like what you get with headlamps, they've gone more like a powdery white, sort of florescent light looking.
 
Any condensation in there is due to moisture being in there, which can only have got in through a faulty seal or a crack. I'm 99% sure you can't check from the bottom. It doesn't take too long to remove the bumper though.
 
Ok, I'll check them out properly, they havent previously misted up before though, only after the first time they've been used.