The reason unopened chips go stale is due to permeability.
The polymers which make up chip bags have tiny spaces between their molecules which are tiny gaps that allow air to slip in and get through the gaps.
The oxygen that reaches the chips in the bags reacts with the chips and causes them to become rancid, stale and even smell eventually.
Chip bags are filled with nitrogen gas to prevent the oxygen in the air from reacting with the chips but after awhile the nitrogen gas slips out and can't protect the chips.
Also water vapor passes through the tiny gaps in chip bags which causes the chips to become stale.
The causes of chips to go stale are the chips absorbing too much moisture from the air and also because once opened the oxygen in the air oxidizes the chips and breaks down the oils which give the chips flavor.
The starch molecules in chips are also hydrophilic which means they attract water from the air.
When chips are left out in the open the chips pull water from the air around them, which leads to the chips becoming stale and less crunchy.
Stale chips are not bad for you as long as they've not actually spoiled and grown bacteria.
Staleness of the chips doesn't mean they've grown bacteria or have become unsafe to eat but when chips are stale they are less enjoyable and less tasty.
It is safe to eat stale chips as long as they've not gone rancid or as long as the stale chips don't taste too bad or smell bad.
If the stale chips smell bad or smell off or taste bad then you should throw them out.
But just because the chips are stale it doesn't mean they're harmful or unsafe to eat.
You should throw away stale chips if they are really stale or when the stale chips are more than a few years out of date.
If the chips are just slightly stale and you don't mind the taste then you can safely eat them.
I eat stale chips as long as they're not really stale but if the chips have gone really stale then I throw the stale chips out.
Eating stale chips won't harm you or make you sick unless they have actually gone bad and grown bacteria.
Expired chips can make you sick if they have actually gone bad but most often the expired chips are safe to eat as long as they've remained sealed.
The expired chips will lose their flavor overtime but remain safe for 1 to 2 years past their expiration date.
At worst you would not like the taste of the expired chips and not want to eat any more of the expired chips or if you did eat chips that have gone bad you may just get an upset stomach.
If the chips are expired and taste really bad then you should throw them out but if they just have lost some of their flavor and are not expired for very long then they are okay and safe to eat and will not make you sick.
You can still eat expired chips.
Chips that are expired may not taste as good as fresh non expired chips but as long as the expired chips have remained sealed the expired chips are safe to eat.
As long as the expired chips don't have any mold or really bad taste to them you can safely eat the expired chips.
There's a discount food store hear in my town that sells foods that are near expiration date or have expired but are safe to eat.
I buy canned foods that are expired or about to expire and even chips that are about to expire or have expired.
I've eaten the expired chips and other expired food and never have gotten sick from it.
While it's best to eat the chips before expiration date you can safely eat them.
When chips have gone bad they will taste really bad and then you wouldn't want to eat them.
Usually though if the chips are only a year or less expired they are still okay to eat.
Once opened a bag of chips will go stale within a few days if you don't seal the bag back up.
Once you open a bag of chips you should use a chip bag clip to seal the bag up.