Fingerprints as Frozen Nematic Fields
1Human fingerprints arise during embryogenesis and persist throughout life. While biochemical mechanisms of ridge initiation and growth are increasingly well understood, the physical principles governing ridge-pattern organisation remain unclear. Here, we show that fingerprint ridges can be treated as a frozen nematic field on a bounded surface, exhibiting long-range orientational order and singularities. Modelling ridge orientation as a two-dimensional nematic director field on the functional contact area of the fingertip, we apply a generalised Poincare-Hopf theorem to derive a topological constraint on permitted configurations. Triradii, loops, and whorls correspond to [Formula], [Formula], and +1 nematic defects, whose total charge is set by surface topology and boundary winding. Across 133 fingerprints from open-access databases, 95.5% satisfy the predicted charge-neutrality condition. Although boundary winding is typically below the idealised value (W{partial}S = 0.71 {+/-} 0.12 vs. W{partial}S {approx}1), fingerprints above a threshold (W{partial}S [≥] 0.6) consistently maintain zero net charge, revealing a coarse-grained realisation of the underlying topological rule. These results identify a mathematical limit on allowable fingerprint configurations and position fingerprints as a passive biological record of nematic order, with topology acting as a fundamental constraint on developmental pattern formation.