It’s 1,5 year past the expiration date. For example, what If I drink the soup with a lot of cayenne pepper past the expiration date added?
Are you talking about dry, ground cayenne pepper? If so, then the answer is “no”. I suspect the date is a “best by” date, not an expiration date per se. Spices lose their potency/flavor over time, so they’re often labeled with a “best by/use by” date simply because they won’t taste the same after a while.
If you’re talking about something else, then I’d need more information.
The volatile oils in the seasoning may have evaporated out leaving the powdered seasoning with little flavor, or an altered flavor that may not taste too good.
If it is dry and not caked the cayenne pepper should be fine to eat, it just may not be as strong or as flavorful as expected.
Ninja strikes as I correct so many misteaks. 
Thank you for answers. Really appreciated.
It was like that:
http://www.masterfoods.com.au/Images/Product/300x300-CayennePepper.jpg
(Bolding mine.) http://www.fsis.usda.gov/Fact_Sheets/Food_Product_Dating/
Other than what might be required under federal and/or state laws for selected food items, food expiration dates are marketing tools.
Judging by how some of the serving staff act about milk where I work, I know a lot of people don’t get the difference between a “sell by” date and an “expiration date”, and I’ll bet that’s what a lot of food companies count on.
For the love of God, it’s fine. It could be 2 decades past its expiration date and it would be fine.
if you have cayenne pepper that old, i suggest throwing away all your spices and starting over as you need them.
Well, it wouldn’t be harmful, but there would be little potency left after two decades.
Would it be theoretically possible for the oils in the spice to undergo rancidifcation?
Not that it’s something I would be particularly (or at all) worried about.
In my family we joke about the stuff in the spice cabinet that only gets used once a year, at Christmas. Some of it has addresses with zone numbers rather than ZIP codes.
When I worked in the kitchen of the local homeless shelter between 1996 and 2004, we occasionally received donations from people who had recently died. Usually this was an elderly person, and their families would clean out their cupboards and bring it all to us. Sometimes, among the canned/boxed food, we’d find stuff that had no UPC symbol. That is, stuff that had been sitting in the deceased’s cupboards since the early-/mid-1970s.
Rancid oils aren’t generally toxic - rancidification is a chemical process, not a biological one, and the results just taste nasty.
I think the biggest danger to the OP’s health is if the pepper has lost its flavour and his dining companions throw the bland soup over him.
When I visited my son and his family a couple of years ago, I noticed a spice rack on the counter; one of those that swivels on its base and has maybe a dozen spices in bottles. They had gotten it for their wedding 12 years earlier. The spices and herbs had all faded to a uniform brownish gray, and many had solidified in the jars. I took the liberty of dumping them all out.
Presumably, they thanked you for your thoughtfulness. Maybe you should have also gone through their closets to toss away clothes that were no longer in fashion. If I had in-laws and they did something like that, I’d be thinking, “Why, I ought to pound you!”
i’ve got some Ferdinand Magellan brand spices. should i get some fresher ones?
I just thought I’d echo this advice. As long as food stays dry, it’s very unlikely to be unhealthy for you regardless of its age. It might taste awful, but all forms of life - and the enzymes in them - require moisture to be active. So you won’t have bacteria, mold, enzymatic decomposition, etc. without some moisture.
Caking is a sign that a powdered ingredient has been wet in the past, even if it is dry currently. If it has ever been wet, you should consider it suspect.
And, powdered spices need not be directly exposed to water from your sink - if you shake the jar over a boiling pot (say, of soup), water vapor can enter the container and cause caking that way, too.
What CC said.
If you then refilled the rack with new spices, you’re awesome. If not, you’re a horrible meddling in-law!
I refilled most of them. They’re barely able to use salt without fucking it up, so I’m sure whatever I put in the jars will still be there in 20 years.