It is likely that this "fog" is caused by flavoured vapours reacting with the plastic on the clearomizer.
Several people have reported specific flavours being behind this problem. Pineapple is the most commonly mentioned "problem" flavour, but here's a more comprehensive list of other flavours that have been know to cause negative reactions with the plastic (be it cracking or fogging):
- Sour flavours
- Citrus acid
- Malic acid
- Cinnamon
- Wintergreen
- Cherry
- Ripe banana
- Honeysuckle
- Cola
- Grape
- Rootbeer
I haven't had the chance to try all these flavours myself, but I have noticed these flavours specifically mentioned in forums like the one here:
Fogging and cracking seems to be more of an issue with smokers who use the plastic vapour tanks. It'd be interesting to here which you use?
Perhaps switching to glass or metal tanks would solve the problem altogether, in which case you'd be free to enjoy whichever flavour you like without having to worry about excessive fogging.
Finally, there is also a chance that parts of the tubing has melted and left vapours behind that might be dangerous to your health. This isn't very common, but if you've been "vaping" for a while with this piece of kit, then it may be time to consider an upgrade.
