For many St. Patrick’s Day revelers, the holiday calls for kelly green clothing and Irish knit sweaters, but for some the following day may be more about feeling green.

The annual holiday’s unofficial dress code hails to Ireland’s nickname the Emerald Isle. The green stripe in the Irish flag is another factor. The green represents the country’s Catholics, whereas the orange stripe odes to the Protestant population and the white stripe symbolizes the peace between the two religions.

Attending the St. Patrick’s Day parade in Aldershot on Friday, the Duchess of Wales and Duchess of Cornwall Kate Middleton broke with tradition, opting for a turquoise suit from the designer Catherine Walker. Her appearance was the first one reviewing the Irish Guards, after having been made colonel of the regiment by King Charles.

However, parade goers in U.S. cities like New York and Boston are known to line the streets dressed in much more relaxed styles. Think rugby shirts, Guinness scarves, Irish caps, plastic green hats, plaid kilts, and more leprechaun-inspired looks like shamrock face paint for the more adventurous.

New York’s St. Patrick’s Day parade dates back to 1762 — 14 years before the signing of the Declaration of Independence. Since the 17th century, some domestic modern revelers are known to be more rambunctious. An estimated 2 million spectators are said to line the 30-block route along Fifth Avenue in Manhattan, where 150,000 participants pass by.

For anyone who may overindulge, a new survey by Lawn Love ranks the best cities to cure a hangover in. To crunch the numbers, the criteria included such factors as Hangover Food, Hangover Drinks, Other Remedies, Getting Home and Sleeping in Public. San Francisco landed the top spot with an overall score of 78.73, followed by Miami, New York, Boston and Washington, D.C. Rounding out the second half of the top 10 were respectively Chicago, Seattle, Jersey City, New Jersey, Philadelphia and Alexandria, Virginia.