Sunglasses anti-fog solutions safe for cycling I wear full sun protection when I ride, including sunglasses and a tube wrap around the lower half of my face.  The issue I have is that in cool weather the wrap tends to channel air from my lungs up through my sunglasses which then fog up.  This is mainly a problem only when climbing hills, as at all other times there is sufficient air flow from my speed to keep my lenses free of fog. Fog obviously obscures my vision and is a safety problem.

At bit of research shows many different anti-fog solutions, including soap, shaving lotion, and special liquids made just for anti-fog.  The problem is, I have not been able to get a clear answer as to whether any of these are safe or suitable for cycling.  The anti-fog liquids seem geared towards things like swimming and diving, as do most of the reviews.  Some of these products list sunglasses as a possible application, but do not say whether they are safe to use given the many sensitive types of coatings some sunglasses already have applied.  In fact, several places I have read claim one should not use certain types of anti-fog coatings as they can affect the plastics in the sunglasses or the anti-reflective coating - it is hardly worthwhile to reduce fog if creates a new problem of reflective glare or the glasses falling apart.

Note that I'm not asking for a recommendation on eye wear as this post is doing.  I already have eyewear I am committed to using, and just want to know what anti-fog solutions (if any) are safe in terms of not degrading anti-reflective coatings, polycarbonates in the glasses, or the plastic in the frames.  

I also already know the trick of breathing out through my mouth and don't want to use this as a long term solution as it makes my throat very dry in a short period of time.

Update: After extensive additional research I have come across a product called "FogTech".  The company claims that the product "contains proprietary self spreading water absorbers dissolved in a very special carrier that can wet plastics... The unique carrier evaporates immediately leaving a transparent micro-thin coating of Fogtech..." and further claims that it is completely safe to use even if the lenses have special coatings.  The only downside is that it is very expensive - as much as $3 for a single application.  Any first hand experiences with this product would be welcome - how well does it work, and more importantly, how long does an application last?
The answer is "they are probably safe" and "they don't work for spit". 

Skiers have exactly this same problem with ski goggles and what I have learned in 50 years of skiing is that if the goggle has an built in anti-fog coating, cleaning it with anything but a mild soap will ruin what minimal anti fog coating 
it has. Sunglasses generally don't have much in the way of anti fog coating. I tried everything I could find and it was all a huge waste of money.

What I have found that has largely fixed the problem for me in skiing is two things. 


Wear a helmet. ( this probably doesn't apply to bike helmets, but ski helmets do a lot to keep the moist warm air from your head away from the goggles. )
Change your jacket. 


When I switched from skiing in a Goretex jacket to a jacket that actually breathes (soft shell) 99% of the goggle fogging problem disappeared. Anything that is a vapor barrier just funnels all the warm moist air from your body directly up into your face. The only WB fabric I've found that comes anywhere close to venting well enough to use with aerobic sports is eVent. 

Applying this to your situation, you need a face mask that breathes better. Either that or one that some how seals to your face at the top. There is no magic goop that will prevent fogging, the only solution is to keep the moist air away from the glasses. 

After you give up attempting to keep your current sunglasses from fogging, you might try a pair of these. 



http://www.xcskistore.com/casco-nordic-spirit-ii-white-nordic-ski-eyewear.html

They are very expensive, wierd looking, but they are by far and away the most fog resistant eyewear available. I've used them biking and for all kinds of skiing and  they just don't fog up ever.