This is a myth. Silicone does not do this. From my post about silicone sex toys and interview with Metis Black:
I own a lot of silicone. Scratch that; I own a lot of quality, true silicone. And I’m not diligent about storage. So if there’s anybody who can say that this is a myth, it’s me. And Metis. I asked her about this and she said:
""I think this came from so many toys that were TPR or TPE that were (and continue to be) mislabeled silicone. Thermoplastic materials melt because they are unstable (they have free electrons that try to bond to other materials). As these electrons leave the toy, the toy disintegrates. No silicone is going to melt. At 600 degrees F it turns ashy. A silicone toy like the O2, with extra soft silicone, may burn off some of the dimethicone – flaming a little and becoming sooty- but still not melting.""
So in other words if your silicone sex toy has any issues in your toybox, then it’s either not truly silicone or some rogue silicone lube from another toy got on it.
Also from that interview she talks about the deal with silicone lube and silicone sex toys. If you are using a quality silicone sex toy and a mid-grade or better lube, you most likely will not have a reaction. As I discussed in my post, Metis told us how to test it. I've successfully used Wet brand lube (both a true silicone lube and a hybrid) on many types/manufacturers of silicone and never had a reaction. So yes, you can still warn people but it's not going to be a Chernobyl-esque meltdown every time. You can pass along the patch test tip, and even try it out for yourself. Silicone lubes are the best to use for bath or shower play (water-based will just not hold up obviously).