You don’t need a special, tiny skin-care fridge—a simple cool, dark place will do. “I typically recommend storing them in a cabinet,” said dermatologist Alexis Stephens. However, dermatologist Luke Maxfield said it’s a good idea to put your vitamin C serum in the fridge (any size, tiny or mighty), if you can commit to the extra step. “Many studies show that the lower the temperature, the longer the lifespan of your vitamin C,” he said.
Prioritize a spot that is protected from both artificial light and sunlight. “UV light is the primary driver of free radical generation and has the greatest capacity to break down your vitamin C,” Maxfield said. He noted that visible light may also be impactful, but it’s less of a concern than UV light when it comes to vitamin C stability.
Beyond heat and light, you’ll also want to make sure your vitamin C serum stays airtight. Vitamin C’s primary function in your skin-care routine is acting as an antioxidant, shielding your skin from damaging free radicals that can contribute to concerns like dark spots, fine lines, and more.
But when vitamin C is exposed to air, that very protection begins to deteriorate, according to Maxfield. “The air consumes vitamin C’s protective capacity, robbing it of the benefits you ultimately want to preserve for your skin.” This is why it’s essential to always seal the bottle tightly, as well as to use the caps or lids that come with your product.
Some manufacturers, such as Timeless Skin Care, are proactive about protection, using opaque, airtight packaging to block out light and air. SkinCeuticals, on the other hand, has a patent on its stability method. That means its serum can remain effective for longer, even when it’s in a dropper bottle that will unavoidably expose the serum to light and air, according to dermatologist Mina Amin.
While protective packaging and formulaic innovations are great, there’s no evidence to suggest they will make your vitamin C serum invincible in a steamy bathroom. And some brands, including Timeless Skin Care, have instructions on the bottle suggesting you store the product in the refrigerator or in another cool, dry place. If you’re choosing a cool, dark place in your bathroom (such as a medicine cabinet or a pull-out drawer), make sure to do a humidity test. After your next hot shower, take a peek at the items in your drawer or cabinet. If they’re dewy and damp or warm to the touch, pick another spot.
This is especially important if your serum contains L-ascorbic acid, the form found in four of the six serums we recommend in our guide. “L-ascorbic acid, one of many forms of vitamin C, is quite unstable,” Maxfield said. “Even while protecting against things like light degradation with an opaque bottle, and protecting it from air, a steamy room will still impact the quality and preservation of the product,” he said. “Steamy implies the combination of heat and humidity, both of which will increase the destruction of your vitamin C product.”
Other forms of vitamin C—like ethyl ascorbic acid, found in the Olay Vitamin C + Peptide serum featured in our guide—are more stable and may require less-meticulous care than L-ascorbic acid, Maxfield said. But that doesn’t mean they’re entirely resistant to degradation. If you want to get the most out of your serum—regardless of the type of vitamin C it contains—it won’t hurt to store it mindfully.
This may sound like a lot of hassle, but it’s important if you want the products you buy to work as intended, for as long as possible. “A product’s stability ensures its effectiveness,” Stephens said. “If a product is unstable, it will not provide benefits to the skin. In the case of destabilized vitamin C, you will not see a reduction in the appearance of hyperpigmentation or promotion of collagen production.”
