What are fingerprints?
Fingerprints are the pattern of the epidermal ridges on fingers. They consist of friction ridge units that can be characterised by patterns (arrangement of ridges) and minutiae (small specific details such as bifurcations and ridge endings).
Examples of minutiae
How do fingerprints arise?
Fingerprints develop during early fetal life. They undergo various phases, of which crucial events occur by the early weeks of the second trimester.
- Fertilisation of egg initiates embryonal development
- Gastrulation – early single ball of cells reorganises into three primary tissues
- Ectoderm – forms the epidermis, including friction ridge skin
- Mesoderm – forms connective tissue of dermis
- Endoderm – forms other major organ systems including gastrointestinal tract, respiratory tract, urinary tract
- Morphogenesis (shape)
- Limbs rapidly develop from about 4 weeks: arms, legs, knees, elbows, fingers, toes seen at about 8 weeks.
- At 7–8 weeks volar pads begin to form from mesoderm
- Volar pads less prominent then disappear; friction ridge units develop
- Volar skin is layered epidermis on top of shapeless fibrous dermis
- Basal layer becomes more prominent and forms folds of epidermis into dermis (primary ridges)
- Volar pad regression and friction ridge development continue; by week 16 permanent minutiae are set.
- Sweat glands and epidermal–dermal ridge system continue to mature and enlarge.
- By end of second trimester, sweat ducts and pores appear along epidermal ridges
- Fetus continues to grow in weight
What are the theories of friction ridge development?
There are two main theories that aim to explain the processes underlying friction ridge formation.
Mechanical instability theory
The mechanical instability theory regards ridge formation as a consequence of a buckling process. Ridges form perpendicular to lines of greatest stress.
- Differential growth of the cellular layers of the skin creates resistive boundary forces, causing a compressive effect.
- The nervous system is also involved in this process.
- Once the interaction of forces is great enough, a buckling instability occurs and further cell proliferation may increase the depth.
The neuro-ectoderm theory describes an interdependent relationship between the neurological map and the pattern of primary ridges.
- The ridges are established upon a grid of sensory nervous tissue. Mapping the volar pad precedes ridge formation.
- Specialised cells such as Merkel cells, certain basal cells and Meissner corpuscles are involved.
- Results in primary and secondary ridge formation with anastomoses.
Clinical relevance of loss of fingerprints
Friction ridges can become thicker and shorter with ageing, and are more difficult to discern.
Loss of fingerprints is sometimes observed in various skin diseases. These include trauma, benign and malignant skin lesions, infections and inflammatory skin conditions
- Bacterial infection such as pyoderma
- Pitted keratolysis
- Tinea manuum
- Herpes simplex
- Viral warts
- Hand dermatitis including Exfoliative keratolysis and pompholyx
- Acanthosis nigricans
- Systemic sclerosis
- Raynaud phenomenon
- Systemic lupus erythematosus
- Epidermolysis bullosa
- Lichen planus
- Pyogenic granuloma
- Erythema multiforme
These skin pathologies can cause disruptions to papillary lines, altering the depth and steepness of the ridges and valleys. This can affect analysis by modern-day biometric pattern recognition systems. This can interfere with the reliability of personal identification methods or "fingerprinting".
Most cases of damage to fingerprints are reversible, as the pathology is relatively superficial. However permanent scarring can occur with deep lesions.