Vitamin C does a lot. As mentioned earlier, it's the body's most major aqueous antioxidant. And because it is most plentiful in the extracellular matrix of your skin, there are a slew of beneficial effects that it brings there:

-- Reducing wrinkles and increasing skin texture and skin tone
-- Suppressing pigmentation of the skin by inhibiting the enzyme tyrosinase
-- Curbing inflammation
-- Bolstering the skin's immune system
-- Enhancing sunscreen protection
-- Increasing levels of tissue inhibitors of collagen-degrading matrix metalloproteinases
-- Thickening the skin
-- Retaining natural moisture

Now, their are four primary characteristics vitamin C possesses that are responsible for these effects.  These are:

1. The prevention of free radical formation Shindo et al. May et al.
2. The protection and treatment of photodamaged skin Darr at al. Lin et al. Perricone. Kobayashi et al.
3. The suppression of pigmentation and decomposition of melanin Kameyama et al
4. The stimulation and regulation of collagen production Nusgens et al. Geesin at al. Hata and Senoo

Antioxidant. Vitamin C is an important antioxidant for your skin since it is crucial for protecting all structures of the cell - both by inactivating free radicals inside the cell and between the cells (which can damage your skin's DNA), and by recycling vitamin E, which will also protect the lipid-soluble structures as well.

More recent research suggests that vitamin C also participates in the pathway that induces cell death by protecting against DNA mutations and by helping to induce death of an unhealthy cell.

Working with Vitamin E. As reported in The Journal of Nutrition, in order for vitamin E to inactivate a free radical it must first absorb the extra electron from the free radical. By doing this, however, the vitamin E molecule is inactivated. And this is where vitamin C comes into play: because vitamin C can recycle vitamin E, it is able to accept the extra electron from the vitamin E molecule, thereby restoring the antioxidant power to vitamin E.  (Study) What's more, several studies have shown increased synergistic benefits from the combination of vitamins C and E together.

In an article published by the Journal of the American Academy of Dermatology, research uncovered two things: 1) that topical application of vitamin C protects skin cells, and 2) and does so with even more protection when combined with vitamin E. The results: skin cell protection from sun burn and decreased molecular indicators of UV-induced photodamage.

UV Protection and Photodamage Treatment. Did you know that exposure to UV light has been shown to decrease naturally occurring vitamin C levels in the skin? The good news is that not only has topical application of vitamin C been shown to have a protective effect against UV-induced sun damage, but it also is able to treat pre-existing photodamage. Moreover, the molecule seems to function also as a sunscreen when applied topically (study).

Here are the hard facts UV protection:

-- In a study of ten volunteers, post-UVB irradiation erythema was reduced in those pretreated with topical vitamin C.
-- In another study on pigs skin, sunburn cell numbers were significantly reduced in treated versus non treated skin.

And here are the hard facts about chronic skin damage:

-- Effects on Photodamaged Skin Topography. Results: Demonstrated improvement in wrinkling, skin tone, tactile roughness and overall assessment of the skin on the side of the face treated with vitamin C in both clinical evaluation and patient feedback.
-- Topical Vitamin C and Vehicle for Rejuvenation of Photodamage. Results: At the end of the three-month study, wrinkling improved and biopsies showed an increase in collagen on the side of the face treated with the vitamin C gel. Additionally, none of showed any signs of inflammation.
-- Vitamin C abrogates the deleterious effects of UVB radiation Results: Topical L-ascorbic acid prevents ultraviolet immunosupression.

Pigmentation. Vitamin C specifically works on decreasing pigment synthesis by inhibiting tyrosinase (a chemical involved in the creation of melanin and skin pigment).

One study concluded that vitamin C does this by suppressing UVB-induced skin pigmentation by the ROS scavenging pathway. Another, suggests that it does so through the decomposition of melanin. Regardless, the skin-lightening effects of vitamin C have been clearly documented.

Collagen. As I'm sure you're all aware, aged skin compared with younger skin shows a decreased baseline production of collagen. What's more, it's also been shown that the tissue concentration of ascorbic acid is significantly reduced in aged and photoaged skin.

The good news is that in vitro studies showed that ascorbic acid, when added to fibroblast cultures from elderly cells, stimulated cell proliferation at the same rate as younger skin cells. Even better: Topical application of vitamin C has been reported to enhance the synthesis of composite elastin fibres and of collagen.

As proposed here, one way vitamin C may stimulate collagen synthesis is by directly and specifically activating collagen gene regulation, both by increasing transcription rate and by stabilizing procollagen mRNA. Another study, published around the same time (1996), points to vitamin C's collagen producing capabilities through its modulation of collagen-synthesizing enzymes and its control of collagen-degrading enzymes like matrix metalloproteinase-2.

In addition to this, numerous other studies have shown that topical vitamin C may have therapeutical effects for partial corrections of the regressive structural changes associated with the aging process (such as the thinning of skin), perhaps through the mechanism of angiogenesis (the formation of new blood vessels) or by increasing the skin's hydration.

Related Posts:

Part 1: What is it? Vitamin C: An Investigation & Discussion

Part 3: What is it? Vitamin C as L-ascorbic acid

Part 4: What is it? Vitamin C derivatives