Recently I've noticed that the nicotine bites my throat. I started out at a nic level of 15 in my nauti tanks and over the past 8 months have lowered my nic level down to 4 in my nauti tanks and 2 in my sub tanks, which I started using a couple months ago. With both tanks the nicotine bites my throat and I have bought juice at different places and it still happens. Why is this now starting to happen?