As was common in military culture of 19th, 20th, and 21st century Earth, Starfleet personnel maintained a quasi-uniform hairstyle. Sideburns were perhaps the most universal aspect of this, as many male officers stylized their sideburns to end in triangular points. Many ships, including the USS Enterprise-D, had barbershops staffed by barbers onboard, where it was likely that this uniform sideburn style was administered. Some male personnel, William T. Riker being notable among them, chose to wear beards as well.
According to Stephen E. Whitfield and Gene Roddenberry's The Making of Star Trek (pp. 286-287), the distinctive pointed sideburns worn by male Starfleet personnel originated as a compromise between Roddenberry's desire to show "futuristic" hairstyles reflective of Star Trek's setting and the actors' objections to the prospect of being required to abandon their favored contemporary styles off camera.
In I Am Spock (p. 28), Leonard Nimoy stated that he had initially suggested pointed sideburns specifically as a Vulcan style for Spock, and quipped that their propagation to other Federation characters was due to Vulcans being "galactic trendsetters." In a 2016 interview with StarTrek.com, Laurel Goodwin further claimed that it was she who had originally suggested the look to Nimoy. 
For Star Trek: The Next Generation and subsequent series, Michael Westmore created several iterations of a document known as the "Side-Burn Bible," or simply "The Bible" for short, illustrating his prescribed technique for makeup artists and hairstylists to artificially create these "pointy sideburns" utilizing crepe wool, which would be trimmed and applied in a manner that blended with performers' natural hair growth. Painting on of makeup was advised against, except to repair holes. (Makeup Man: From Rocky to Star Trek, pp. 204-205)
Several examples of performers who had their sideburns added on by the makeup department include:
- Abdullah bin al-Hussein's appearance as a lieutenant of the sciences division aboard Voyager in VOY: "Investigations".
- Through several seasons of Star Trek: Deep Space Nine, sideburns were reportedly the only aspect of makeup that Kenneth Marshall required for his portrayal of Michael Eddington. (The Official Star Trek: Deep Space Nine Magazine issue 15, p. 55)
- While portraying Phillip Green in the Star Trek: Enterprise episode "Demons", Steve Rankin reported the following about his makeup process: "They made me up, got my hair dark, gave me the pointy sideburns."