Prince William and Princess Catherine were married April 29, 2011 in what some call the most anticipated wedding of the century. The couple engaged in not one, but two very proper and very public royal kisses on the balcony of Buckingham Palace after their ceremony in front of about 2 billion viewers worldwide.
So, why does kissing feel so good? Researchers from Lafayette College in Pennsylvania may have uncovered the answer. They found lip-locking actually sparks an increase of hormones in the brain. Due to a series of complex chemical processes, those involved in kissing experience a combination of relaxation, excitement and love, according to the study.
Actress Nicole Kidman and singer Keith Urban kiss during a match between Federer and Robredo at the U.S. Open tennis championship in New York on Sept. 7, 2009.
By the way, did you know that holding hands and kissing reduces the levels of the stress hormone cortisol? So if you're feeling stressed, pucker up!
Actresses Ellen DeGeneres and Portia de Rossi kiss after Ellen won outstanding talk show host for "The Ellen DeGeneres Show" at the 35th Annual Daytime Emmy Awards at the Kodak theatre in Hollywood on June 20, 2008.
Humans aren't the the only ones that kiss. Great Apes press their lips together when they're excited and want to show affection.
U.S. President Barack Obama kisses his wife Michelle as they dance at the Eastern Regional Inaugural Ball in Washington, D.C. on Jan. 21, 2009.
What's the difference between a simple peck and a passionate kiss? Well, a little peck only uses two facial muscles while a full-on kiss uses all 34 muscles in your face.
Mariah Carey and Nick Cannon kiss on the red carpet at the 82nd Academy Awards in Hollywood on March 7, 2010.
Which side do you like better, the left or the right? It seems couples prefer the right since two out of every three couples turn their heads to the right when they kiss.
Actress Katie Holmes is greeted by her husband actor Tom Cruise holding their daughter Suri, after Holmes finished the 2007 New York City Marathon in New York on Nov. 4, 2007.
And while this kiss is pretty proper, it seems men like it a little sloppier, according to scientists.
"There is evidence that saliva has testosterone in it," said Rutgers University anthropologist Helen Fisher, and testosterone increases sex drive. "And there is evidence that men like sloppier kisses with more open mouth. That suggests they are unconsciously trying to transfer testosterone to stimulate sex drive in women."
Singer Justin Bieber kisses his girlfriend, singer Selena Gomez, as they arrive at the 2011 American Music Awards in Los Angeles November 20, 2011.
According to Fisher, men could also be using the saliva transfer to assess women's fertility and estrogen cycle, but they might want to be wary of turning women off with too much slobber.
Jada Pinkett-Smith kisses her husband Will Smith as the Los Angeles Lakers play the Boston Celtics in Los Angeles on June 12, 2008.
And here's another fun fact for you. More than 90 percent of human societies exchange smooches, according to Fisher.
Country singer Faith Hill and her husband Tim McGraw kiss backstage at the 43rd annual Grammy Awards in Los Angeles on February 21, 2001. The duo won Best Country Collaboration With Vocals for the song "Let's Make Love," while Hill won two additional Grammys for her album "Breathe."
While some anthropologists think that kissing originated as a way for mothers to transfer pre-chewed food to their children, others theorize that kissing started out as a gesture of fusion or union of souls.
Actors Angelina Jolie and Brad Pitt kiss at the 14th annual Screen Actors Guild Awards in Los Angeles on Jan. 27, 2008.
One study found that 66 percent of women and 59 percent of men say that the quality of the first kiss can kill a relationship, Fisher said.
Why does kissing feel so good? We have the answer... and some examples of celebs who love to lip-lock in public