Turn on your television, flip through a magazine, log online and there’s Beyoncé posing for L’Oreal, Jennifer Hudson promoting Weight Watchers, and Martin Scorsese for the iPhone. A celebrity endorsement campaign can generate a buzz, distinguish a product from its competitors and connect a brand to its target market. Accordingly, professional athletes, actresses and musicians are often called upon to lend their status of success and glamor to influence product sales.

With about 15% of U.S. ads featuring a celebrity spokesperson, several campaigns have garnered iconic status over the years. Nike, which operates much of its advertising through celebrity endorsements, famously paired up with Michael Jordan for a career-long sponsorship deal and the launch of the “Air Jordan” brand. Pepsi has had a string of music-industry sponsors over the years, ranging from Michael Jackson in 1980s and 90s, to current spokeswoman Nicki Minaj. Unsolicited product recommendations from Oprah Winfrey, a trusted public figure and Forbes’s “Most Influential Celebrity.” have caused brands such as Spanx shapewear to “become bestsellers and pop-culture phenomena.”

The challenge for brands is to identify celebrity associations that will prove most effective. Ozzy Osbourne’s campaign for I Can’t Believe its Not Butter and Justin Bieber’s for OPI nail polish have received criticism because the celebrity may be considered “irrelevant” to the product. Much like enlisting a sports-legend to promote athletic gear, successful campaigns attempt to closely match public figures to their respective demographic. Therefore, brands should “consider age, image, strategic brand alignment” and the public’s perception when selecting a sponsor.

Endorsement deals may fall through if a celebrity’s persona does not fit the brand’s image. Just recently, Rihanna’s campaign for skincare brand Nivea was terminated when she was deemed too provocative to represent Nivea’s values of “trust, family and reliability.” In 2009, after his scandalous private life was revealed to the public, Tiger Woods’ “ranking among celebrity endorsers tumbled,” according to the Davie Brown Index, which measures potential influence and consumer perceptions. More concretely, reports put shareholder’s losses from his several endorsement deals at an estimated $12 billion.

Despite the potential risks, companies seem to take great stock in a celebrity endorsement’s ability to promote their product. In the social-media driven age, brands are shelling out $10,000 to Kim Kardashian for posting a single tweet endorsing their product. This year, actress Sofia Vergara, of ABC’s Modern Family, earned the title of Forbes’s top paid television actress after signing endorsement deals with Pepsi, COVERGIRL, Kmart and Burger King.

From a consumer perspective, such expensive marketing efforts may not, in fact, increase demand. A 2011 poll showed 77% of respondents were not more likely to purchase a product if backed by a celebrity; even more extreme was the 14% that said a celebrity endorsement would make them less likely to buy a product.

American advertising continually reflects our celebrity-geared culture. While sponsors and campaigns come and go with the times, “A-list” endorsement deals endure as a fixture of the advertising industry. They can elevate a brand or degrade it—whatever the result, a celebrity endorsement, most importantly, is sure to be noticed.