I am a big fan of that superhero skin care ingredient, 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.

Sunday is Vitamin C Day, thanks to SkinCeuticals (makers of the widely acclaimed C E Ferulic Serum), which first recognized April 4 as National Vitamin C Day in 2019. (The registrar at National Day Calendar proclaimed the day to be an annual observation.)

Why do 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 fight free radicals to keep your skin bright and glowy.

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 screens. They can cause dark spots, dullness, wrinkles and even skin damage. Unfairly and like everything else, it becomes even harder to fight the effects of free radicals as we age. Antioxidants such as vitamin C protect skin from free radicals, which also makes vitamin C an ideal booster to your sunscreen. (This is why I apply my vitamin C serum in my morning routine, after cleansing and toning and before moisturizing.)

While you can find vitamin C in tons of products, a vitamin C serum will give you the most bang for your buck.

The only downfall is that vitamin C is notoriously unstable, which means products containing it are prone to go bad faster than your other products. The more vitamin C is exposed to air or light, the less potent it becomes. It could irritate your skin but, mostly, it won’t do its job, which just means your vitamin C product immediately becomes a waste of money.

You’ll want to find a vitamin C product with air-tight and dark or opaque packaging. You also should store it in a cool, dark and dry place, aka not a humid bathroom. I like to keep mine in a drawer in a bedroom, like an underwear drawer — this way, you never forget to apply it.

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

You also want to find a vitamin C product that will work for your specific skin type and concern. Thankfully, there’s no shortage of products and brands to choose from.

For example, SkinCeuticals offers three vitamin C serums for every skin type and concern. The original, SkinCeuticals C E Ferulic serum, reduces the appearance of fine lines and wrinkles, firms skin and brightens its complexion. SkinCeuticals Phloretin CF serum treats slightly more severe hyperpigmentation, such as uneven skin tone, post-acne marks and melasma.

The most recent addition to its vitamin C family is SkinCeuticals Silymarin CF, a serum designed specifically for oily and blemish-prone skin that combined 15% L-ascorbic acid (a form of vitamin C), 0.5% salicylic acid (a beta hydroxy acid great for curbing breakouts and oil over-production) as well as 0.5% silymarin and 0.5% ferulic acid, both of which are powerful antioxidants. Silymarin CF not only works to neutralize free radicals but also can reduce skin oiliness, refine skin texture and visibly improve signs of aging, including fine lines and dark spots.

In addition to SkinCeuticals, Summer Fridays CC Me Serum is a favorite of mine with opaque glass packaging, a pump top and a packed collection of skin-strengthening peptides, (vegan) squalane to lock in moisture and two forms of vitamin C. Tatcha Violet-C Brightening Serum, meanwhile, is 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 well 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 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 its fans love. If you’re sensitive to fragrances and dyes, something like Drunk Elephant C-Firma Day Serum or Beautycounter Counter+ All Bright C Serum would be perfect for you.

The options above are pricey, but especially with vitamin C, 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. Pacifica Glow Baby Super Lit Booster Serum also won’t break the bank. It contains sodium ascorbyl phosphate, a form of vitamin C that’s gentler and more stable than its counterparts, and glycolic acid that carries an added benefit of gentle exfoliation for smooth, glowing skin.

Vitamin C is an important step in your skin care routine, and with so many brands and options, you can definitely find the right one for your preference, concerns and budget.