Fingerprint Ridge Density Reveals Sex Differences in Young Adults from North India

Fingerprints left on a window, a knife handle or a car steering wheel can do more than identify a suspect. According to a new study of young adults in North India, the sheer number of friction ridges packed into a small square of print differs consistently between women and men, offering investigators a probabilistic clue about who left an impression when no matching print exists in any database. The research, published in the Egyptian Journal of Forensic Sciences, examined fingerprint ridge density, defined as the number of ridges crossing the diagonal of a 5 mm by 5 mm square, in 113 participants aged 18 to 30 years from District Ludhiana in the Punjab state of North India.

The study team, led by Tej Kaur with senior author Kewal Krishan, collected inked, rolled fingerprint exemplars from all ten fingers of 56 males and 57 females, yielding 1,130 prints in total. Participants were recruited through a combination of purposive and convenience sampling after giving informed consent. Healthy individuals between 18 and 30 years were included, while anyone with fingertip injuries, deformities, skin conditions or unwillingness to consent was excluded. Each print was labelled systematically for the thumb, index, middle, ring and little fingers of both hands, and ridge counting followed the standardized ink method described by Cummins and Midlo, with uniform pressure and controlled rolling to capture complete nail-to-nail impressions.

The technical core of the work lies in its topological approach. Rather than reducing each print to a single number, the researchers divided every fingerprint into three regions: the radial side, the ulnar side and the proximal area, positioned with reference to perpendicular axes drawn through the core of the pattern. Using a linen tester magnifier at 10X magnification, a single trained observer counted the ridges intersecting the diagonal of the defined square in each region. All measurements were taken three times for each participant to reduce intra-observer error, and the final value was averaged. Accidental fingerprint patterns were excluded because they lack a consistently identifiable core, and complex patterns such as whorls and composites were handled by consistently selecting the most central or proximal core.

The results were unambiguous in direction. Females exhibited higher ridge density values than males across all 30 parameters examined. Among males, the highest mean value appeared in the Right Ring Proximal zone at 14.165 with a standard deviation of 1.604, while the lowest was in the Right Little Ulnar zone at 8.036. Among females, the highest mean was recorded in the Left Ring Radial zone at 15.632, and the lowest again in the Right Little Ulnar zone at 9.145. The minimum ridge count of 5 ridges per 25 square millimetres appeared in multiple proximal regions in both sexes, reflecting the generally lower ridge densities of proximal areas compared with the distal radial and ulnar zones.

Statistical rigour was a deliberate feature of the analysis. Because 30 variables were compared simultaneously, the authors applied a Bonferroni correction, dividing the conventional significance level of 0.05 by 30 to obtain an adjusted threshold of 0.00167. After this correction, 21 of the 30 parameters retained statistically significant differences between the sexes. Six variables, including the left middle radial and right middle ulnar zones, remained significant at the conventional 0.05 level but not after correction, while three parameters, the right index ulnar, right ring proximal and right thumb ulnar zones, were not significant at any threshold. Normality was assessed with the Shapiro-Wilk test, and six normally distributed parameters were analysed with independent samples t-tests while the remaining 24 were analysed with the Mann-Whitney U test.

The strongest single difference emerged in the left little finger radial zone, where males averaged 13.143 ridges and females 15.035, a difference yielding a t statistic of minus 5.616 and a p value below 0.001. The left ring finger ulnar and radial zones followed closely. Proximal zones also contributed meaningfully, with significant results in the right middle, right index, left little, left middle and left index proximal regions. Notably, several of the non-significant parameters clustered on the right hand, a pattern the authors interpret as possible laterality in the expression of sexual dimorphism, though they caution that this warrants confirmation in larger samples.

Effect sizes added a second layer of evidence. Using Cohen’s d for the parametric variables and Cliff’s delta for the non-parametric ones, the team found large effects in nine regions: the right middle radial, right middle proximal, left thumb radial, left thumb ulnar, left index ulnar, left middle ulnar, left ring radial, left ring ulnar and left little radial areas. Twelve parameters showed medium effects and nine showed negligible to small effects. The uniformly negative direction of all effect sizes confirmed the pattern of higher ridge density in females, and the left hand generally produced larger effect magnitudes than the right across comparable finger positions, reinforcing the laterality observation.

Measurement reliability was assessed by repeating ridge counts on the same subjects after a one-month interval. The percentage error ranged from 0.1 percent to 0.9 percent, within limits considered acceptable in anthropometric research, with right-hand errors of 0.55 percent radial, 0.14 percent ulnar and 0.1 percent proximal, and left-hand errors of 0.27 percent radial, 0.64 percent ulnar and 0.86 percent proximal. The authors themselves note, however, that percentage error offers only a limited evaluation of reproducibility, and they recommend that future studies report more robust statistics such as the intraclass correlation coefficient or technical error of measurement.

The forensic logic behind the work is specific. Fingerprint individualisation in casework rests on minutiae comparison, and ridge density serves instead as a complementary morphometric tool within biological profiling. It becomes valuable precisely when traditional identification is impossible: when only a partial print is available, when no suspect database match exists, or when the investigative goal is profiling sex, age or ancestry rather than positive identification. In such scenarios, estimating the sex of the person who left the print can narrow the suspect pool by roughly half. Prior research has established population-specific thresholds, including Acree’s classic finding that prints with 11 or fewer ridges per 25 square millimetres are most likely of male origin and 12 or more most likely female, and the authors stress that absolute ridge density values vary markedly between ethnic groups, making population-specific reference databases essential.

The study’s limitations are candidly enumerated. The sample was small and drawn from a single district, limiting generalizability. Bilateral symmetry analysis was not performed, fingerprint pattern type was not controlled, and in real casework latent impressions often arrive without known orientation to a specific hand or finger, which may limit the standalone investigative value of inter-finger differences. Ridge density is also influenced by ethnicity, age, stature, finger width and body weight, with inter-ethnic variability reported to exceed inter-sex variability. The authors emphasise that ridge density is a probabilistic indicator rather than a definitive tool for sex determination, that effect size does not establish classification accuracy, and that future work incorporating predictive analyses such as ROC curves, sensitivity and specificity, along with larger and more diverse samples, will be needed to fully evaluate the discriminatory utility of fingerprint ridge density in forensic sex estimation.

Subject of Research: Sexual dimorphism in fingerprint ridge density among young adults in North India and its forensic relevance

Article Title: A study of fingerprint ridge density amongst young adults of north India– sexual dimorphism and forensic aspects

Article References: Kaur, T., Kaur, N., Siwan, D., Chitara, N., Sharma, S., Sharma, V., & Krishan, K. (2026). A study of fingerprint ridge density amongst young adults of north India– sexual dimorphism and forensic aspects. Egyptian Journal of Forensic Sciences, 16(1), Article 77. https://doi.org/10.1186/s41935-026-00577-y

Image Credits: AI Generated

DOI: 10.1186/s41935-026-00577-y

Keywords: fingerprint ridge density, sexual dimorphism, forensic science, dermatoglyphics, sex estimation, North India, biological profiling, ridge counting, effect size, latent fingerprints, fingerprint, ridge