Forensic methods
Types of fingerprints: loops, whorls and arches explained
The three fingerprint patterns, how common each one is, the ridge details examiners actually compare, and how prints are found and identified at a crime scene.
Forensic Science Pakistan2 min read
Every fingerprint is made of friction ridges, the raised lines on the skin of the fingers and palms. Their overall flow falls into three pattern types, which examiners use to classify prints, while the small details inside the ridges are what make a print unique.
The three fingerprint patterns
Loops
Ridges enter from one side, curve around a core and leave on the same side. A loop that opens towards the little finger is an ulnar loop; one that opens towards the thumb is a radial loop. Loops have one delta, the triangular point where ridges meet.
Whorls
Ridges form circles or spirals around a central point and have two deltas. Subtypes include the plain whorl, the central pocket loop, the double loop and the accidental whorl.
Arches
Ridges flow from one side to the other with a rise in the middle and no delta. A tented arch rises sharply to a point.
How common is each pattern?
Loops are the most common pattern and arches the rarest. In a study of 8,000 fingers, loops made up 55.9%, whorls 34.9%, arches 6.1% and composite patterns 3.1%. Frequencies vary between populations and between fingers, so popular figures such as “65% loops” are only rough averages.
What examiners actually compare
Pattern type alone cannot identify anyone, because millions of people share each pattern. Identification rests on minutiae, the points where individual ridges end, split or form small features:
- Ridge ending: a ridge that stops.
- Bifurcation: a ridge that splits into two.
- Dot or island: a very short ridge.
- Enclosure (lake): a ridge that splits and rejoins.
Even identical twins, who share the same DNA profile, have different fingerprints, because ridge detail forms under random pressures in the womb.
Prints found at a crime scene
- Patent prints: visible marks left in blood, ink, paint or dirt.
- Latent prints: invisible marks of sweat and oils that must be developed.
- Plastic prints: impressions pressed into soft material such as wax, putty or soap.
Latent prints are developed with powders on smooth surfaces, chemicals such as ninhydrin on paper, and superglue (cyanoacrylate) fuming on plastics and metals. Each developed print is photographed and lifted, and logged in the chain of custody before it leaves the scene.
How a fingerprint is identified
- Analysis: the examiner judges whether the mark has enough clear detail to compare.
- Comparison: the mark is compared side by side with known prints, often shortlisted by an automated fingerprint identification system (AFIS).
- Evaluation: the examiner decides whether the mark is an identification, an exclusion or inconclusive.
- Verification: a second examiner repeats the comparison independently.
This process is known as ACE-V. Fingerprints are one of several branches of forensic science, and are often combined with DNA from the same touch traces.
