When Leonard DiCaprio bought his Greenwich Village residence (for a cool $10 million in 2014), he redid the plumbing so that his showers sprayed out vitamin C-infused water.

That may seem like money down the drain, but a less-drenching topical application of vitamin C can help slow or even reverse the signs of sun damage and aging, such as wrinkles and dull, saggy skin.

One study published in the journal Nutrients found that applying vitamin C formula for three months reduced fine and coarse wrinkles on the face and neck, and improved skin texture.

Another study in the Journal of the American College of Dermatology found that when topical vitamin C is combined with vitamin E that’s stabilized with ferulic acid, it reduces skin redness and protects against sun damage.

For teens, one study found that the topical application of sodium L-ascorbyl-2-phosphate — a stable vitamin C derivative — helps manage acne.

If you're shopping for a vitamin C serum, buy it directly from your dermatologist or a verified online retailer. The formula should contain an active form of vitamin C (for instance, L-ascorbic acid), have a strength of 10% to 20%, and a pH lower than 3.5. Apply it at night.

But to get the full range of skin benefits from vitamin C, various studies have demonstrated that you also have to ingest 75 mg to 90 mg daily; the upper daily intake for adults is 2,000 mg from fruits and vegetables and, if necessary, supplements.