Updated Sept 2019: Added photos at the end for Paula’s Choice C15 Super Booster comparing serum I recently opened to the serum after ~2 months of no refrigeration.

Updated May 2019: I’ve added photos at the end for Paula’s Choice C15 Super Booster.

Updated May 2018: I’ve added a photo a 4 month (120 days) photo of the Drunk Elephant C-Firma Day Serum.

Updated April 2018: I’ve added a photo comparing Drunk Elephant’s C-Firma Day Serum that has been opened for 30/60/90 days.

Updated March 2018: I’ve added photos at the end of this post of Drunk Elephant’s C-Firma Day serum that has been open for 2 months.

Updated October 2017: I’ve added photos at the end of this post of Skinceuticals CE Ferulic that was stored in the refrigerator for around 7 months.

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I’ve used SkinCeuticals CE Ferulic serum for many years and it would turn darker over time in the bottle. Because I didn’t know any better, I’d use it up until it was gone. Then, I read online that when it changes color and oxidizes you shouldn’t use it on your face. So after throwing out 1/2 of a very expensive bottle, I decided to look for cheaper alternatives.

I read that some folks had very good luck storing their serums in the fridge and taking out smaller quantities at a time to store in their bathrooms for daily use. Refrigerating the serums kept them clear over many many months. After reading that some bloggers had success with Timeless 20% C &E serum and that Timeless guarantees their product to stay fresh for 3 months, I bought it.

After using it for 6 months, I decided to stop using products with alcohol in them (fatty alcohols were the exception). My guess is that the Timeless C&E serum has such a tiny amount of alcohol in it that it doesn’t dry the skin but I wasn’t taking any chances.

I then purchased Cosmetic Skin Solutions Vitamin C & E serum because it is a duplicate for SkinCeuticals CE Ferulic serum in terms of ingredients, although the pH level is higher (although still acidic). And unlike the Timeless serum, it doesn’t include (possibly) drying alcohol as an ingredient. But, I was worried it might oxidize over time even if I kept it in the fridge.

Here are the results…

I started using Cosmetics Skin Solutions almost 6 months ago on Feb 24th.

Here’s what it looks like today. In-person, it actually looks a bit more clear than the photo. I’m pretty happy with this result and will continue to use it.

Also, even though lots and lots of bloggers have reported the pH level, I thought I’d test it to see. The pH value of Cosmetic Skin Solutions Vitamin C+E looks to be around 3.5, still acidic enough for the product to work.

Also, for those of you who use the Timeless serum, here’s what it looks like after being stored in my fridge for 1 year, looks like I opened it on August 20, 2015:

Update on Timeless serum December 2020: This has become my go-to vitamin C serum after I had a bad reaction to Paula’s Choice. I wrote a full review of Timeless here.

Update October 16, 2017: My best friend has been doing an experiment with Skinceuticals CE Ferulic. Although she forgot to take a before picture, below is what it looks like after being stored in the refrigerator since late March 2017, so around 7 months. She says that the color has not changed and it was not clear when she opened it. A quick google search tells me that this color is normal.

Update March 2018: In January, I decided to try Drunk Elephant’s C-Firma Day Serum because I felt like I needed something a bit more moisturizing for winter. I like the serum enough but am not sure I’d use it in the summer. I think it might be too thick/moisturizing even though my cheeks/chin are dehydrated/dry.

For about 1 month, I kept the serum in my bathroom cabinet. But then I noticed it changing color so decided to put it in the refrigerator. Unfortunately, I wasn’t smart enough to take a pic at that time so I don’t know if this has changed color even more or not.

I read that the founder of Drunk Elephant said there is no benefit to refrigerating the serum. I’m skeptical because she wants to make a profit, it is a business after all so she might say that even if she doesn’t know because she hasn’t tested it. And if she didn’t care about profits, she’d lower her prices and keep the products exactly the same. So that is why I decided to refrigerate it to see what happens.

Note: I do one pump per day and twist it closed after using it. I do this based upon other blog posts I’ve read and have no idea if it actually prevents oxidation or not. I will update with pics again in a couple of months….or sooner…I’m not sure how much longer it will last.

Below is a photo that includes 90 days. I’m not sure I’ll have enough to make it to 120 days but if I do, I’ll post an update. To me, the 60 and 90 days look very similar. Especially considering the lighting and angles aren’t the same.

This is likely my final update, below is a photo comparing 3 months and 4 months.  The 4 month photo is definitely darker. Also, please know that I use vitamin c serum only in the morning. This is because I use curology in the evening and my formula includes vitamin C. (I love curology and if I could only use one product/service, it would be their tretinoin serum. [UPDATE: Due to curology changing their inactive ingredients, I now use Musely. Feel free to use my referral code for 30% off your first Face-Rx order: MR0630). If I could only use one product/service, it would be their tretinoin cream!)]

Update Nov 2018: I no longer use the drunk elephant firma C. After I was finished with the one bottle, I went back to using the Cosmetic Skin Solutions C+ E. I really like that this serum is similar to Skinceuticals but costs a lot less.

Update May 2019: Cosmetic Skin Solutions discontinued their Vitamin C+E serum so in February, I started using Paula’s Choice C15 booster. Not my favorite brand at all but I like this serum and my review is here.

February 8 is the day I opened it. On May 7th, I had only a tiny amount left so I decanted what was left into a sample-size bottle. I think the serum looks the same after three months as on day 1.

Update September 2019: I’m still using Paula’s Choice C15 Booster. Severals months ago, I decided to not refrigerate the serum to see what would happen. It definitely darkened but I still felt comfortable enough to use it. My bottle was nearly empty on July 8th so I don’t have any additional photos.