Question on lens storage and dry air (Drying the air)

So in humid areas people want to prevent mold. The best way is lack of moisture. So people suggest silica gel desiccant/dryers. But I have seen quite a few times here in posts that silica gel can dry out lubricants and rubber seals/gaskets if its use is overdone. This does not make sense to me. So can somebody explain how this would occur and more importantly provide links (preferably scientific links) that would prove of these effects?

My reasoning is as follows. If the lubricant is neither a vapor (it is not a vapor) nor becoming a vapor (which it should not be doing anyway unless the lens is at temperatures that would melt any plastics on and in the lens and is no longer a lubricant) and the silica gel is not being directly mixed with the lubricant, how can it dry out the lubricant? Also the use of a water based lubricant should not be appropriate in the manufacturing of a camera lens so I am doubting they use water based lubricants in lens manufacturing - so that too should not be a factor.

So a silica gel pack should therefore only affect the moisture in the air that comes in contact with. Lubricants are not in the air. This is also why the silica gel packs are more effective if you can get the air circulating around them and the area they are to dry.

What about the silica gel affecting the rubber to dry out the seals/gaskets and other plastic/rubber parts? Being rubber does not dry out it reacts. It can react with solvents and other chemicals. Most of the time the drying and cracking or other adverse affects are caused by oxidation. That is the natural process that the oxygen in the atmosphere does to almost anything and everything (think rust, verdigris, tarnish, the browning of a cut apple, etc….).

I know some rubbers have plastisizers in them that can leave over time and make them brittle (“dry-out”) over time. My understanding that this drying is usually caused by heat, excessive UV radiation, and/or ozone damage – so how would the silica gel do these?

So the closest explanation would be that the drier air would have more oxygen so there can be more oxidation. (Dry air holds more oxygen than humid air.) Yet, the increase in oxygen in dry air would (I doubt) hardly be significant enough to make much of a difference in the oxidative process compared to a slightly more humid environment.

Also I can’t imagine, short of just about covering your equipment in silica gel, that you would get much below a 25% humidity level with the silica gel packs. So unless someone can explain, it seems to me it would be better to have the air reasonably dry as possible, if the desire is to prevent mold, and that the dry air should not be a problem for a lens. And that it would be too hard to get such a low humidity that static would be a problem with the equipment.

So please help! Others and I would like to keep our lenses in the best possible storage environment. Does anyone know the ideal humidity level for digital camera electronics and camera lenses? (Real data not hearsay!)

Also/Or does anybody have any direct evidence that the silica gel (or overly dry air – say 25% humidity) has caused a problem with their lenses or cameras?

I've never heard of silica drying out seals. Not only that, I use silica in my safe and have for years and I've never had a problem. If I were you, I wouldn't worry about it.....it sounds like you're overthinking it.

Have kept all my vintage camera collection, slides, large format negatives, for more than 30 years - in a sealed box over-packed with silica gel packs. I inspect al contents once a year in minute detail. I have to date not noticed any such effects you mention. Even some rubber hoods after 25 years of storage do not exhibit any dry rot.
So my answer is no, but I do have evidence it works just fine.

I have a few photog friends lives in high humidity places like Singapore and Malaysia, they use dry box that looked like a mini fridge with dehumidifier in it, they use them for lens storage, I also came across a DiY dry box awhile back that you can put together easily for cheap, check this out:

http://www.squidoo.com​/diy-dry-box

Silica gel doesn't draw out all the humidity anyway. It takes it down to about 40%. (source)