A. There is a no black and white answer to this question as there are various factors which will affect how long your ski helmet lasts. How often is your helmet used? How is it stored? How much UV damage has it sustained? Has your helmet been damaged from falling over?
If you rarely go skiing, it hasn’t received any damage and it was only a short trip you will find your helmet will last much longer.However if you are a regular skier, due to the UV damage you would need to replace your helmet a lot more frequently. Most people would replace their ski helmet after 2 or 3 ski seasons. If your helmet has any damage whatsoever it is safest to replace your helmet immediately.
When your helmet is not in use it needs to be stored away from any UV damage, so usually in the bottom of a cupboard or wardrobe is a safe place. A special helmet case will help prevent your helmet from getting damaged when in transit or when stored.