How long a product will last depends on several factors, including how chemically stable it is. Simple, solid inorganic substances, like salt, will remain unchanged for a long time, while man-made substances won’t.
However, environment factors are a concern, too. Temperature changes, exposure to air, water, humidity and sunlight can trigger chemical reactions, leading a substance to degrade or change into a form that is either ineffective or even harmful.
Products in metal containers where corrosion has occurred, or in plastic containers that are swollen, shouldn’t be used. Separation, sediment or changes in color, consistency or odor are red flags.
Pay attention to expiration dates. While some reputable companies provide expiration or “best if used by” dates voluntarily, most won’t unless they’re required to do so, as it’s not to their advantage to tell you how “fresh” a product is. If the product is expired, toss it.
No one wants to waste money on products they don’t need, but no one wants to risk their own or an animal’s health either.
Use common sense, check for expiration dates and conditions of storage, observe for physical changes and when in doubt call the manufacturer for advice. The more we ask these types of questions, the more likely manufacturers will give in and put the information on the label — where it belongs.
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”Shelf Life Chart”