How to Tell If Your Vitamin C Serum Has Gone Bad

December 19, 2023
Sarah Ferguson
By: Sarah Ferguson | by L'Oréal
Dropper applicator with a drop of liquid

Vitamin C is a star ingredient in countless dermatologists, estheticians and skincare lovers’ books. It’s a powerful antioxidant that helps protect skin from free radical damage, and as a result, prevents premature signs of aging from forming. Vitamin C (known as L-ascorbic acid in its pure form) is also known to fade dark spots and even out skin tone and texture for a brighter complexion. 

Our only complaint about vitamin C is that it’s unstable; this means it can degrade and oxidize over time and lose efficacy. Factors like light, air, heat and humidity can all speed up the oxidation process. But how can you tell if your vitamin C serum has gone bad? We asked Dr. Elizabeth Houshmad, a board-certified dermatologist based in Dallas to find out. 

How to Know if Your Vitamin C Serum Has Gone Bad

The biggest red flag is if the color of your vitamin C serum has changed over time. “If it is completely yellow, brown, orange or any shade other than what it looked like when you first bought it, it most likely has gone bad,” says Dr. Houshmand. If you’re still unsure, take note of any scent or texture changes, which may also be a sign that it’s time for a fresh serum. While she says there’s no harm in using an oxidized vitamin C serum, you’re not going to be reaping all of its many benefits. We also recommend reading the directions and descriptions of your skincare products — brands will often explain what your serum is supposed to look like.

How Can You Prevent Your Vitamin C Serum From Going Bad? 

“Your best option is to use the vitamin C product within a three-month time period,” says Dr. Houshmand, noting that the average vitamin C serum lasts for three to four months before it expires. Most serums have PAO, or period after opening, symbol on their packaging, which indicates when they should be used by or when they “expire.”  

“You can also keep your product away from heat and light,” Dr. Houshmand adds. This is why we swear by keeping our vitamin C serums in the refrigerator — or at the very least, tucked away in a dark drawer. 

Choosing a vitamin C serum with a certain type of packaging can also help prolong the shelf life. Dr. Houshmand recommends looking for a dark, opaque glass bottle with a protective seal. Two options are the Kiehl’s Powerful-Strength Vitamin C Serum and the skinbetter science Alto Defense Serum; both feature a pump applicator to keep the formulas fresh and safe from air exposure. Another option at a drugstore price point is the L’Oréal Paris Revitalift Derm Intensives Vitamin C Serum, which is housed in an airtight metal tube to prevent exposure to oxygen and light. 

Kiehl’s Powerful-Strength Vitamin C Serum

There are also vitamin C powders, like the Exponent Beauty Brightening Boost Vitamin C Power System, which comes with a separate serum to mix with the vitamin C powder to create your own stabilized formula. Note that L-ascorbic acid has been found to be more stable in powder form than serum form, per the National Center for Biotechnology Information

Ultimately, the best way to prevent your vitamin C serum from going bad is to use it within the three to four month time frame. Buy your vitamin C serum as needed (rather than stocking up on a few at once), so you’re always introducing a fresh formula to your routine.

Additional Reporting By: Reece Andavolgyi Photographer: Chaunte Vaughn

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