Members of the Deltan race, both male and female, were bald and had the ability to ease pain in others through touch.
They were also a very sexually active species, with their pheromones and sub-conscious telepathy enhancing their appearance to non-Deltans. Because of this, Deltans serving in Starfleet and other positions dealing with other species took an oath of celibacy. (Star Trek: The Motion Picture)
The ECS Horizon met some Deltans in 2141. Travis Mayweather later expressed, while they were very attractive and honest, the Deltans affected him, and he combated this by excessively working out in the gymnasium. (ENT: "Bound")
A female Deltan served aboard the USS Excelsior in 2285, while a year later, a male Deltan was an ambassador serving on the Federation Council. (Star Trek III: The Search for Spock; Star Trek IV: The Voyage Home)
Anara Rysyl was a Deltan Starfleet officer serving as the operations manager aboard the USS Sutherland from 2371 until 2376. She felt the Deltan oath of celibacy was archaic and discriminatory. (Star Trek: Sutherland)
In 2372, a Deltan crew and Paragon officer Kate Howard died aboard a Deltan ship after the Romulans planted a "crystalizing" virus aboard. Fellow Paragon officer Timothy Garrick was the only survivor. (Star Trek: Paragon: "The Captain's Day Off")