Pubmed, Science direct data bases were used while some information were collected by direct searching using Google search engine. Reference lists of identified articles were explored for additional articles. Certain keywords were used alone or in combination which form the headings and subheading of the articles. In maintaining the focus of the review original research and reviewed articles were included. Case report and abstracts, editorial were excluded.
The epidermal ridge pattern depends upon the cornified layer of epidermis and dermal pattern. Proliferation of cells in the lower zone of epidermis resulted in projections in the dermis as regular spaced thickenings. The dermisalso projects upwards into the epidermal hollows, referred to as dermal papillae. This led to appearance of elevations on the surface of the skin known as epidermal ridges.
The crucial events for the establishment of the epidermal ridge pattern take place from the 10th to 16th weeks of development. At 10th week, embryonal volar skin consists of the layered epidermis on top of more amorphous fibrous dermis. At that moment the epidermis consists of three layers; periderm on the outside, the intermediate layer and the basal layer at the interface of the dermis.
During 11th week the basal layer of the epidermis consists of columnar cells whose axis is perpendicular to the skin surface. It’s observed that the basal layer becomes undulated, which quickly becomes prominent and form folds of the epidermis into dermis. These folds are called primary ridges which establish the future surface patterns which become well pronounced at the 16th week. Because fingerprints patterns are encoded at the interface between dermis, the pattern cannot be destroyed by superficial skin injuries.
Primary ridge formation does not occur simultaneously on volar skin surface. The formation usually starts at a certain area in the middle of volar pad (which is called the ridge anlage) and along nail furrow, a little later along the interphalangeal flexion creases. The area of the ridge anlage usually coincides with the center of the whorl and loops if such pattern shows up. In this way, there are three ridge system on the fingertips (starting from the ridge anlage, the nail furrow and the flexion creases), which slowly spread over the fingertip. At the location where these ridge systems finally meet, triradii arises.
It’s likely from empirical evidence that the primary ridge system changes until the 16th week, when it becomes permanent. For example, it was observed that the number of minutiae significantly rises in that time. A possible reason for this observation could be a large growth rate of the finger compared with bridge of the ridges, which will lead to the insertion of new ridges as minutiae.
The different hypotheses were established which are key to the understanding of the embryology of the fingerprints. Although there is no general consensus on the mechanism for ridge formation to date, the following hypotheses in
| Hypotheses | Mechanism | Limitation |
| Folding and mechanical processes |
Folding process, which is induced by differential growth and the process, is parallel to the largest growth stress. | The sources of stress that produces the observed patterns not identify. |
| Intense cell proliferation in the basal layer of the epidermis resulting in cylindrical cells, which evade the stress by folding toward the dermis. | ||
| Nerve |
Fingertips are innervated by hexagonal pattern of axons whose wavelength roughly equals to the one of fingerprints. | A ridge direction and ridge formation has still been observed in experiments where innervations was prevented. |
| Fibroblast |
Fibroblast cell pattern are similar to fingerprints pattern, thus it formation is induced by pre pattern of the fibroblast in the dermis. | What induced the formation of the pre pattern of the fibroblast in the dermis not clear |
| Biochemical |
The repetition of the pattern was due to a specialized biochemical system (morphogens) allowing formation of the wrinkles in the fingerprints. | The exact influence of each biochemical and mechanical factors on the formation of surface pattern becomes an experimental challenge. |
Several features are associated with fingerprints. The formation of fingerprints feature is influenced by several factors in utero. These factors can be summarized as follows
| Factors | Definition | Features | Comments |
| Volar pads |
Temporary eminences of the skin surface that form during the 7th week of development | Pattern | · Highly rounds symmetrical pads whorls; |
| · Less well developed asymmetric pad shows loops | |||
| · Pad slanted to the right give rise to loop opening to the left and vice versa. | |||
| · Small indistinct pads (flat pad) give rise to arches. | |||
| Boundaries |
Nail furrow, flexion creases and margin of the fingertips | Pattern | · Act as obstacles to expansion and greatest stress form perpendicular to these obstacles. |
| Markel cells |
Epiderrmal cell which are in contact with nerve endings | Minutiae | · The location of the Merkel cells determines minutiae |
| Genetic |
Gene mutation and protein expression | Ridges | · Proper expression of SMARCAD1 may be important to ridge formation, and the disruption of its expression causes adermatoglyphia. |
The main driving force of using fingerprints is the uniqueness and consistency once formed.
The fingerprints have features which can be used to determine the sex of individuals. Using fingerprint patterns, it was reported that females have more arches, and males have more whorls. Males’ prints tend to have higher levels of urea than women's.
A population-wise comparison demonstrated that ridge densities recorded amongAfricans (Sudanese and Nigerians).
Gelatine based tape and high-tech chemical analysis under spectroscopic microscope reveals the chemical- and metabolic make-up found on a fingerprint. The study revealed that specific amino acids indicated whether the “suspect” was a vegetarian ormeat-eater.
The earliest scientist to explore the potential of fingerprints in clinical medicine was Cummins.