You wear a helmet to be extra safe. Why would you wear a damages helmet? Might as well stick with a beanie that's lighter and more comfortable in that case.
17 Jones Storm Chaser . 17 Never Summer Proto Type Two . 16 Never Summer Swift . 16 Rome Pow Division ST x Snurfer . 16 Gnu Swallow Tail Carver . 15 NS Snowtrooper BIA . 15 Jones Hovercraft
16 Burton Genesis X . 15 Now Drive
16 Flow Talon . 14 Flow Hylite
I think even if you just have a really hard impact but dont see any cracks, its still recommended to buy a new one.
100%, read any helmet manual and it'll say that after any impact it needs to be changed.
That said I bonk my head quite often against trees, sometimes the snow, rocks. I haven't changed helmets yet because I haven't seen any damage yet to any part of the helmet. Even all those little bonks are making me think it's time to get a new one again soon...