coney serums are artificially made hence the silicones in them.
They also usually have preservatives in them to make them last. I don't know if silicones themselves have a shelf life or not .
You could open it and smell it. Even do a strand test but honestly, after 5 years I'd just toss it and buy another. Probably what you'll find is the silicones absorb the plastic the containers made of so no matter how nice the serum used to smell like they often end up smelling like the plastic it came in. This is one of those questions where the person really has to see touch and smell the product before answering.
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