Keith Flamer of Forbes magazine just published an article entitled "Vitamin C Showers (And Other New-Age Amenities) Trending In Hotels." This article was similar to an ABC News report about vitamin C shower filters in Las Vegas hotel rooms back in 2013.
According to Forbes, here's the idea: "Vitamin C-infused showers neutralize chlorine and enhance shower water with an essential nutrient and antioxidant that leaves guests with healthier hair, skin and nails."
Let's look at the facts here. Do these Vitamin C shower filters really neutralize chlorine? Do they "enhance" shower water?
First, off, I suspect that these filters do neutralize chlorine that is in the shower water. For this purpose, the mechanism makes sense. See picture from Stay Well's website below. Chlorinated municipal water goes into the device, where a small amount of vitamin C is added, thereby neutralizing the chlorine. (Here, I actually like they they use the word "reduced," which is the correct scientific term -- the vitamin C reduces the chlorine oxidant.)
Now, how could we test to make sure this thing is working? Easily. Buy a chlorine test kit from the pool supply store and test the water that comes out. Is there chlorine in there? I suspect that this thing probably neutralizes ("reduces") the chlorine in municipal tap water.... until the cartridge runs out. All else aside, this is good. You should prefer showering in chlorine-free water.
Here's the downside: These cartridges are pretty expensive and probably don't "enhance" shower water much at all.
These cartridges go for about $65 each and they don't have much vitamin C inside. To get the benefits of vitamin C, you want to use lots of it. And, it's difficult and expensive to provide significant amounts of vitamin C. This is why vitamin C serums are so expensive.
Think about it: how much vitamin C do you think you could fit inside that little cartridge? How long could that possibly last? (Again, you could test for yourself, as described above). If I had to bet, I would say that these Stay Well cartridges have less than half the vitamin C that we put into one 6 oz bottle of SwimSpray.
Bottom line: I suspect that these cartridges provide chlorine-free water for the lifetime of the cartridge. But, given the mass of the cartridge, I highly doubt that it provides enough vitamin C to provide any other of vitamin C's benefits, such as anti-aging, etc..