How long does a cycle helmet last? BBC Radio 4 (Melanie Abbot) speaks with Jay Lewis at Velorution, in central London about the "shelf life" of the products, deterioration of the EPS over a number of years - impact resistance lost, and could fail. Manufacturers state anything between 2-5 years. Ann Hayes British standards suggests that you check manufacturers instructions, but a maximum of five years as a precautionary practice; of course any impact damage should lead to replacing the helmet.
But if your helmet looks like this then maybe it's time for a change - something that fits better and can survive a number of impacts!