The term ‘dermal’ refers roughly to the surface of the skin. ‘Epidermal’, by contrast, refers to protrusions above the surface of the skin. Thus growth of a mustache or beard is sometimes called ‘epidermal’ growth. One can think of the dermis as the ‘inner’ layer of skin, and the epidermis as the ‘outer’ layer. As far as fingerprints are concerned, the difference between the dermal and the epidermal is of significance for the relative forensic value of each sort of fingerprint. Generally speaking, epidermal prints are more distinctive and therefore easier to match uniquely to a suspect’s prints than are dermal fingerprints. If one thinks intuitively about making an impression in a substance such as wet clay, the difference is that the epidermal impression will be deeper and therefore contain more information than a dermal impression.
This difference translates directly into a difference in permanence if one thinks about the ways in which latent fingerprints corrode and decay (Jain 1997, 1368). A ‘latent’ fingerprint essentially refers to fingerprints that have been left, usually by suspected criminals, by chance rather than by design. Such fingerprints can be whole or partial. So an entire thumb- or finger-print might be left on some object or surface, or a perpetrator might leave only a partial print—the least usable of which is sometimes referred to as a mere ‘smudge’. Obviously whole prints are superior to partial prints for purposes of identifying the perpetrator of a crime.
From this perspective, the crucial difference between dermal and epidermal fingerprints is essentially that the latter are deeper impressions, and therefore—as indicated above—leave more ‘information’ for the investigator to work from. Dermal fingerprints, containing less information, are more susceptible to decay. In conclusion, epidermal prints typically have a much greater permanence than do dermal fingerprints.
- Jain, A. K., Hong, L., Pankanti, S., & Bolle, R. (1997). An identity-authentication system using fingerprints. Proceedings of the IEEE, 85(9), 1365-1388. Online. http://cse.msu.edu/biometrics