The most common form of Tiefling in Khorvaire are the Planetouched, and these are the tieflings that people in Khorvaire are most likely to be familiar with. The planes of Eberron influence the world in innumerous ways, and the people within, and occasionally a child will be born that has been affected by the influence of one of the planes. Planetouched can be formed from any aspect of a plane, positive aspects tend to produce Aasimar, elemental forces produce Genasi, and the malevolent aspects of a plane can produce tieflings.
Each plane influences people in different ways, and the tieflings produced are all distinct from those of other planes. Every plane can produce planetouched tieflings, with the exceptions of Dal Quor and Irian. The former because it has been cut off completely from Eberron, and the latter because it lacks any native fiends.
The cause of a planetouched tiefling's birth is not always clear. Most of the time it might be traced to a manifest zone, or a coterminous period occuring during the pregnancy, but sometimes it seems to just be chance. Some of the planes are more likely to produce tieflings than others, and most planetouched tieflings can trace their origins back to Shavarath, Risia and Mabar. Tieflings touched by Xoriat are incredibly rare, even by the standards of an already small population.