Vitamin C (VC) is a vital nutrient that effectively combats scurvy and plays a versatile role in skincare.

Most Vitamin C serums on the market start clear but gradually turn orange-yellow over time. Many people often questioned, "Has it expired? Can discolored Vitamin C serum still be used?"

Oxidation is the primary cause of this change in color. When opening a bottle of Vitamin C serum, the Vitamin C reacts with the air's oxygen, converting into dehydro-L-ascorbic acid, and eventually oxidizing further into diketogulonic acid, which is orange.

Thus, the darker the serum, the less Vitamin C it contains. However, there's no scientific proof that oxidized Vitamin C harms the skin. Yet, its effectiveness diminishes.

To counteract oxidation, most serums include antioxidants like Vitamin E or ferulic acid. When buying Vitamin C serum, look for antioxidants and compare shelf lives. Since light speeds up Vitamin C oxidation, store your serum in a cool, dark place.

Vitamin C's Benefits:

Vitamin C promotes collagen production by activating a skin enzyme needed during collagen synthesis. This leads to resilient, plumper skin. Thus, Vitamin C is a powerful anti-aging ally. Also, Vitamin C behaves like a milder glycolic acid, aiding in exfoliation.

The Root Cause of Oxidative Discoloration in Vitamin C:

Vitamin C's enediol structure and strong reducing properties make it prone to air oxidation, leading to color changes and loss of effectiveness. Avoid long-term storage at home and take tablets that turned yellow. Use brown glass bottles stored in a light-proof, airtight, dry place.

To use Vitamin C correctly, consider the following:

1. Usage Time:

Vitamin C can be used during the day without concern. Unlike some chemical sunscreens, VC isn't photosensitive and doesn't harm skin after UV exposure. Temporary darkening after VC use is due to oxidized yellow residue on the skin's surface, which easily washes off.

2. Choosing the Right Concentration:

Vitamin C concentrations of 0.6% or higher are effective. Generally, a 10%-20% concentration shows significant results, but it can also be more irritating. Start with 3-5% concentration and gradually increase to find what suits your skin.

3. Combining Vitamin C with Other Ingredients:

Vitamin C pairs well with certain ingredients, enhancing their effects. The classic pairing is with Vitamin E, which boosts antioxidants. However, avoid combining VC with acidic ingredients like niacinamide due to VC's low pH.

Vitamin C's potential against scurvy and in skincare is undeniable. Despite color changes, oxidized VC isn't proven harmful to the skin but becomes less effective. To prolong effectiveness, store serums properly and seek those with antioxidants. Mastering Vitamin C's correct usage and combination can lead to healthier, glowing skin.