The problem with Neosporin, Vetericyn, Vaseline, etc., is that they don't work. Many of you suspect it or already have experience with it, but they are actually very bad for frostbite.
They are all very GOOD for open wounds that are at risk of infection, and I think somewhere along the line someone confused a frostbite burn with an open wound and started to use vaseline to take care of it. But it does more harm than good. And if you think about it, your chickens aren't very likely to get an infection even on an open wound in temperatures so far below freezing anyway - the germs outside of their body probably aren't alive anymore! So when they get frostbite, there really isn't any need to treat it with any sort of liquid - until the temperature warms back up.
But all of these products are a form of liquid. Liquid is a very good heat conductor. Metal is another example. Heat conductor means heat moves THROUGH them very well. In winter, that means it transfers the heat to other objects (such as the air) much faster, and thus loses heat. In summer, they take in the heat from the sun faster than the air itself does. That's why a glass of water sitting in the sun will be warmer than the air around it. That's also why your car door handles (made of metal) seem to be much hotter in summer sun, or colder in winter - and why they aren't so bad when in the shade (because it's the sun's heat they are absorbing, not the air).
So heat conductors are good at TRANSFERRING heat. Both absorbing it, and dispersing it.
Frostbite is where - for some reason or another - the blood has stopped circulating in the area, and the cold has officially frozen that spot. The cold itself could be the reason it froze over - the blood vessels just couldn't keep up with the falling temperatures. But it could also be something else - like a recent injury damaging the blood vessels, which caused low or no circulation until the freezing temperatures set in on it.
When you put liquids on a frostbitten area, the liquid tries to TRANSFER the heat. It absorbs it from the comb, and tries to put it in the cooler air. It tries to even things out. This, of course, is very bad for your chicken's comb! Now add to that, the fact that water needs heat to evaporate, and you can see where this spells disaster for your frostbitten chicken! Any liquid you put on them, is going to try it's best to take heat from their comb, either to evaporate, or to transfer it to the air.
One of the absolute best things you can do to a frostbitten comb is actually to cover it in a powder, like baby powder. This will help it to actually stay DRY, which allows the heat to stay in, and the blood vessels can do their work of keeping up with the circulation. Powder will also help absorb any sweat the chickens may have in their comb, so their own sweat won't encourage more frostbite. Aside from that, nothing can help except simple heat (DRY heat).
And again, if frostbite actually causes an open wound later on, wait until it gets warmer to treat it.