cyclezen

Good thread.
Helmets are about as variable as anything designed for human use. My activities almost all have helmets as a major element of safety/protection.
'Science' as relates to educating, testing or discovering is an important thing, but it's not infallible. It is limited in scope because there's no way to completely cover the complexity of 'real' life/situations. So we need to make our decisions, with the aid of science findings.
Maybe you've seen, as I have, that quite strong/dense packaging foam deteriorates fairly quickly with just some short term time in the sun/environment. So it's not really a long life material.
Sure, it's covered and protected by a shell - but not completely. The environmental conditions still affect the primary 'cushioning' material.
Given 'science', the balance of various expert recommendations, good fit and comfort, wear and tear, I tend to keep my helmets for a while. But I'd rather 'retire' a helmet, than 'Test' the longevity while in actual 'use'.
And I do a couple things to encourage 'longevity'. A Helmet used for 4-5 rides gets a 'shower' with me, and a tiny bit of shampoo for the pads. I have 5 cycling helmets in use at any one period.
They vary for type of coverage, a few have either fixed visor and 2 have a flexible, flip up/down visor for those rides when low sun is probable. Helmets for when most ventilation is needed and helmets for cooler rides. Rotating helmets gives them longer life spans.
Given the difficulty of me finding a good fitting helmet, I'll buy 2 when one proves to be excellent - and put the 2nd in my closet, for later use.
I'm not one who needs 'new' every year, or even 2, 3 or 4 yrs, but I have replaced pads, especially the forehead pad - that one seems to go south, sooner.
It's your ride... and your head.
Ride On
Yuri