There is a substantial degree of genetic influence on one’s fingerprints, particularly whether a given finger has which of the three basic patters—loop, arch, or whorl. One can have all three of these types among the ten fingers. The Scientific American article cited at bottom describes what determines which of these three basic patterns a finger will develop, having to do with the genetically influenced timing of fetal development of the fleshy volar pads on the fingertips.

However, the fine details that make each person unique, called the minutiae of the fingerprints, are not hereditary. Even monozygotic (supposedly identical) twins don’t have identical fingerprints. The minutiae arise randomly in the developing fetus, at least partially as an effect of surfaces the fetus touches while its skin is developing. They arise especially between weeks 10 and 15, so they’re established by birth and don’t change significantly after that.

Abundant sweat glands open by pores along these ridges. The oil of a fingerprint comes not from the sweat, but from other surfaces one has touched such as the facial skin and hair. Freshly washed hands leave less conspicuous or detectable fingerprints—but I wouldn’t advise safe crackers and home burglars to rely on that strategy alone for leaving no evidence.

One is an anti-slip function.

It’s not just a passive effect of absorbing water, but an adaptive neural response.

A second function of friction ridges is tactile sensitivity. These are relatively large (1–2 mm long), with a single sensory dendrite wrapped in layers of fibroblasts and Schwann cells. When you drag your fingertips across a surface, the friction ridges alternately drag and slip. That creates vibrations that stimulate these lamellar corpuscles more effectively.