Question: How do I know if my vitamin C serum has gone bad?
Answer:
The best way to tell if your vitamin C treatment has gone bad is to smell the product and check out its color.
If the serum is completely yellow, brown, orange, or any color other than its normal color, it has probably gone bad. Sometimes the product at the tip can be oxidized (or darker) and you can wipe that part away and continue to use the rest of the C serum, but if the entire product has changed colors, it's time to throw it away.
How the vitamin C product smells is also an indication of its freshness. If it smells weird, funky, sour, or rancid, the C treatment is no longer good and should not be used.
To prevent vitamin C products from going bad, it's best to store C serums in dark glass bottles or metal tubes, away sunlight and heat. They must also be tightly sealed after each application to prevent oxidation.
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