Putting Vicks on your feet helps to make you feel cooler especially when you're having hot flashes or a fever.
Although the Vicks doesn't actually make the fever go down or the temperature of the hot flashes go down but applying some Vicks to your feet helps you feel cooler due to the cooling affect it has on the body.
The cooling affect on your body comes from the camphor and menthol in the Vicks but it doesn't do much but it does make you feel cooler at least temporarily which is a good thing.
I add some Vicks to my feet when I'm having a fever or hot flashes and my body does feel cooler at least for a few hours so it's worth it.