It's not a great idea
Coca-cola has a couple utilities beyond being an accompaniment to burgers and fries. You can use it to make a pretty great Coca-Cola cake, and it's acidic enough to clean pennies. But one thing that Coke can't do, no matter how many internet commenters are claiming it can, is serve as a replacement for tanning oil. Yes, people are using Coca-Cola as tanning oil, according to multiple beauty magazines, and it's just as bad an idea as it sounds. Tanning is already a dangerous practice, given how damaging the sun's UV rays are to the human epidermis. Speeding it up using a fizzy cola is both not smart and pretty gross.
The idea, which gained steam in the UK last year, is that you apply the soda all over before going out in the sun, and the caramel dye in the soda will speed up the tanning process. But actually what's happening, according to dermatologist Joshua Zeichner who spoke to Allure about Coca-cola tanning, is that the acid in the soda is exfoliating dead cells, increasing your risk for a sunburn. The soda merely leads to a temporary darkening of the skin. "While some feel that Coca-Cola can speed up your tan, it actually can be dangerous, and I recommend staying away from it," Zeichner said
Sunburn, in addition to being absolutely no fun, can also increase your risk of skin cancers and wrinkles. Not to mention the whole itchy, burning sensation, and the looking like a lobster thing. If you want a tan, the only safe way to get that bronze glow is from a bottle—just not a bottle of soda. In the meantime, grab some SPF 50 and get out in the sun. Save the fizzy soda drinks for the cooler.