Tissue Growth

• Thumbprints are different for each person due to each person's tissue growth. Tissue growth is individual and based on a person's genetics. Because no two people are genetically identical, even identical twins, the tissue growth will vary, causing different whorls, arches and other patterns in a thumbprint.
  
  

Random Local Events

• When a fetus is developing, completely random local events can occur that cause variation in fingerprints. Studies on quintuplets show that, while these identical children have very similar fingerprints, they are not exactly the same. Random local events can consist of anything during gestation. Because each baby is not in the exact same position, they will develop ever so slightly different.
  
  

Life Experience

• The activities and events of life can alter fingerprints. If you slice your fingertip, for example, scar tissue forms as the finger heals. Because no two people go through life exactly the same way, their bodies are different and the expression of their genes will alter. This leads to differences, even between twins, which in turn can lead to differences in thumbprints.