A superhero skin care ingredient, I am a big fan of vitamin C.

And if you have dark spots, acne scarring, hyperpigmentation, dull skin, uneven skin tone or just feel like your skin isn’t as tight and bouncy as it used to be, vitamin C can help.

Saturday, April 4, is Vitamin C Day, thanks to SkinCeuticals (makers of the widely acclaimed C E Ferulic Serum), who first recognized April 4 as National Vitamin C Day last year. Registrar at National Day Calendar proclaimed the day now be observed annually.

Here’s why we love vitamin C.

In addition to fading dark spots, evening out skin tone and boosting collagen production (which equals bouncy skin,) it also is an essential antioxidant that works to keep your skin bright and glowy.

Vitamin C is an antioxidant. What does that mean?

Skin care, like any industry that makes money, is a lot of marketing and buzzwords, but there are real things that can do amazing things for our skin, like antioxidants.

The air is filled with free radicals, which are molecules that come from everything from the sun’s rays, pollution and cigarette smoke to blue light, like that from our smartphones and other screens we sit in front of all day long.

Free radicals are unstable atoms. If you think back to high school chemistry, unstable atoms mean its outer shell is not full. These unstable atoms want to bond with other atoms, using the new atom’s electrons to fill its shell.

When free radicals are in the air, its basically a search-and-destroy mission: they seek the molecules in your skin to bond to. Too much of this bonding causes “oxidative stress” in skin which leads to dark spots, dullness and wrinkles and even skin damage. Unfairly and like everything else, it becomes even harder to fight the effects of free radicals as we age.

That’s where antioxidants come in.

Antioxidants prevent the effects of free radicals by giving up an electron to the free radical, which stabilizes it and lessens the chances it will damage your skin. This also makes vitamin C an ideal booster to your sunscreen (which you should be wearing daily.) Due to this, I apply my vitamin C products in my morning routine.

Vitamin C is notoriously unstable. Here’s how to address that.

Vitamin C is extremely and inherently unstable, which means that it’s prone to go bad faster than your other products. The more vitamin C is exposed to air or light, the less potent it becomes. You want to find a vitamin C with air-tight packaging (so try to avoid jars or, cleansers that you’re rinsing down the drain for that matter) or those that come in dark or opaque packaging. You also should store it in a cool, dark and dry place.

If you’ve had the product for a while and it’s turned a different color (a yellow to a dark orange), it smells weird or it’s all of a sudden causing a reaction on you face, it’s probably turned. Throw it away immediately.

These are some skin care products that contain vitamin C

In addition to SkinCeuticals C E Ferulic Serum, there’s plenty of products with vitamin C you can try.

 Summer Fridays CC Me Serum is my new favorite with opaque glass packaging, a pump and packed with skin-strengthening peptides, (vegan) squalane to lock-in moisture and two forms of vitamin C. Tatcha Violet-C Brightening Serum, made with 20% vitamin C and 10% AHAs, for both brightening and gentle exfoliation. Lancôme Visionnaire Skin Solutions 15% Pure Vitamin C Correcting Concentrate works incredibly and has great (not to mention luxurious) packaging to preserve the integrity of the serum.

Sometimes it comes down to preference. Cult favorite OleHenriksen Truth Serum is a vitamin C OG, made with the brand’s own blend of stable vitamin C derivatives. It also contains orange extract to give off a fresh, citrusy scent that most lovers of this serum have cited as their favorite part. Conversely, if your skin is reactive or you’re sensitive to smells, something like Drunk Elephant C-Firma Day Serum  would be perfect for you since it’s formulated without any dyes or fragrances (natural or synthetic), as well as without a host of other ingredients the brand deems problematic for some skin. (aka the “Suspicious Six“)

These options above are pricey but you’re paying for potency and packaging. Vitamin C that works doesn’t leave a ton of room for bargain hunting but CeraVe Skin Renewing Vitamin C Face Serum With Hyaluronic Acid is an affordable find. You also can go a different route with Vitamin C powders or capsules since they offer more stability. The Ordinary Vitamin C Suspension 23% + HA Spheres 2% contains tiny balls of vitamin C that burst when applied to skin. It feels gritty and not very luxurious but it’s an affordable option at $5.80.

Vitamin C also comes in the form of eye cream (Drunk Elephant C-Tango Multivitamin Eye Cream) or in masks (Murad Intensive-C Radiance Peel.)

What if my skin hates vitamin C?

Unfortunately, allergic reactions to vitamin C-infused skin care products are pretty common, including red bumps and itchy skin after application. In some cases, users have seen clogged pores and breakouts due to the infamously unstable ingredient’s need to be suspended in silicone.

For those allergic to vitamin C, there’s plenty more ways to reap its skin-brightening and antioxidant benefits. Look for brightening ingredients such as niacinamide (like that found in Peter Thomas Roth’s PRO Strength Niacinamide Discoloration Treatment), alpha arbutin (such as The Ordinary Alpha Arbutin 2% + HA serum) and broccoli seed oil (try L:A Bruket 167 Broccoli seed serum) as well as antioxidants such as vitamin A (retinoids like Drunk Elephant A-Passioni 1% Retinol Cream), Manuka honey (Kiehl’s Pure Vitality Skin Renewing Cream), vitamin E (The Body Shop Vitamin E Overnight Serum-in-oil) and Coenzyme Q10 aka CoQ10 (try Eminence Organic Skin Care Eight Greens Youth Serum) are suitable alternatives.