Usually it doesn't. My dive knife wouldn't rust after being immersed in salt water all day long. All I had to do was rinse it off at the end of the day. Salt water is very corrosive. Immerse a carbon steel knife in salt water for 20 mins and pull it out and it will start rusting right away. I have never seen a stainless steel razor blade rust. Even the carbon steel blades didn't rust when I used them.
Here is an interesting article: http://www.gilletteadjustable.com/contact-us.html It says in part: "After discovering in his test lab that shavers could not tell the difference in blade sharpness, he was responsible for break-thru research that determined that blade sharpness was not a critical factor in receiving a good shave; rather a reduction in drag by hair clinging to the blade causing pulling was needed. This Drag Theory lead to the development of coated razor blades and specifically the Organosiloxane Gel coated Super Blue Blade (1959)." The truth might be that there is more than one reason blades are coated. For example, to enhance blade longevity when in use and to reduce drag. That website has an incredible wealth of information about Gillette adjustables, much more than I have seen anywhere else.
Strange, since platinum is considered hypoallergenic. It's very rare for someone to be allergic to it. It just means that the teflon will come apart at the cutting edge and will thin and slide back along the blade as it is used. It's very difficult to get teflon to stick to things. It's why people in the shaving community usually say that the teflon coating is gone after the first shave. After reading these posts, I'm tempted to just start saying any benefits teflon offers to the shave are probably gone after the first use. I did forget to mention that chrome and platinum are used to harden the edge in my earlier post, I imagine it's because my primitive hind brain was whispering "that's probably marketing BS." I still believe that the factory edge grind and stropping has more to do with how a blade shaves than any coating. Fun fact, the metal used for razor blades is rarely used in knives, and is considered unsuitable, due to it's extreme hardness and tendancy to chip in kitchen use conditions.
I just acquired 5 sealed packs of NOS Autostrop “Rustless” carbon steel blades. I opened one pack and unwrapped one to use. The blade was immaculate. What coating do you think was used? How old do you think they are? I’m going to soak them in barbicide for 10 mins before using. Sent from my iPad using Tapatalk
This Popular Science article from the February 1970 issue, page 60 gives a very good description of blade coatings and their purpose: https://books.google.com/books?id=VQEAAAAAMBAJ&lpg=PA61&pg=PA60#v=onepage&q&f=true Notice that the article says that "Gillette's Platinum-Plus blades are five for $1", or 20 cents each. It also states that a pack of five Wilkinson premium blades are 79 cents, or just under 16 cents each. Fifty years later, Gillette Rubie and Gillette Platinum blades, both premium products, are about 25 cents each. That is amazing, and means they are far more affordable than they were 50 years ago. Here is an example of the equipment used to sputter coatings onto razor blades, in case anyone is interested: https://www.svs.co.uk/razor-blade Also, Bruce Everiss' excellent article on razor blade manufacturing: https://www.bruceonshaving.com/2010/11/09/how-double-edged-razor-blades-are-made/
I came across this article and thought some folks might find it interesting to read. https://www.transparencymarketresearch.com/razor-blade-coatings-market.html
A lot of the blades out of that facility are made on the same machines, I'm not sure what they have going on now because a company that makes machines that make DE blades came out with a new fully automated machine that is much smaller and cheap compared to the big monsters that were traditionally used, so I'm assuming some companies will find it better to get these new machines because the machine does everything down to packing the blades. But PPI in Russia used to run 4 machines with one back up from what one of their employees stated. So different brands are made on the same machine but with different coatings, and some are the same just different names and packaging, it's been awhile since reading anything but if I remember permasharp and sputnik are the same exact blade.