[Antennas] Old Coax

[Lefczik, Larry D]

I've seen several times that coax cable should be replaced after a few
years.  Why is this?  Is it just because of UV exposure to the outer jacket?
If so, is coax which is still on a spool good forever?  Is coax used indoors
subject to aging?  What about MIL-STD coax, is that less susceptible to
aging?  

A lot of questions, but the main question is, why is it recommended to
replace coax periodically?

Thanks de WA2EHZ