Vitamin C serum has become a popular skincare product due to its ability to brighten the skin, reduce the appearance of fine lines and wrinkles, and even out skin tone.

However, it's important to know when vitamin C serum expires to ensure that you're getting the most out of its benefits.

Here's what you need to know:

Firstly, it's important to understand that vitamin C is a highly unstable ingredient and can easily become ineffective if not stored properly. When exposed to air and light, vitamin C can oxidize, losing its potency and effectiveness. That's why it's important to choose a vitamin C serum that comes in an opaque, airtight bottle to protect it from light and air.

Most vitamin C serums have a shelf life of 6 to 12 months from the date of manufacture. However, once the serum is opened, its shelf life can be significantly reduced due to exposure to air and light. That's why it's important to use your vitamin C serum within 3 months of opening it to ensure that you're getting the full benefits of the product.

To determine the expiration date of your vitamin C serum, check the product label or packaging for the date of manufacture or the "best by" date. If the serum has been opened, you can also look for signs of oxidation, such as a change in color from clear to yellow or brown. If you notice any changes in color, texture, or smell, it's best to discard the serum and replace it with a fresh bottle.

To extend the shelf life of your vitamin C serum, it's important to store it properly. Keep it in a cool, dry place away from direct sunlight and heat. Avoid storing it in the bathroom, as the humidity and temperature fluctuations can also affect its stability.

In conclusion, vitamin C serum is a highly effective skincare product, but it's important to use it within its expiration date to ensure that you're getting the most out of its benefits. Most vitamin C serums have a shelf life of 6 to 12 months from the date of manufacture, but once opened, the serum should be used within 3 months. To extend the shelf life of your serum, store it in a cool, dry place away from direct sunlight and heat, and make sure to choose a product that comes in a dark, airtight bottle. 

By following these tips, you can ensure that your vitamin C serum stays fresh and effective for as long as possible.