Facts of lifeA mystery called fingerprints [Archives:2005/863/Health]

July 28 2005

By Dr. Khaled alNsour
For the Yemen Times

Every day we see a new case of how the police or security use fingerprints in discovering the identity of suspects and criminals. It is a known fact that every individual has a unique finger print even if skin on fingertips are injured fingerprint grow back to form the same pattern as before.

New skin usually keeps the old pattern. That swirling, looping pattern of ridges and furrows on fingertip skin that forms a fingerprint usually stays with a person for life – from formation in the mother's womb to death. Gangster John Dillinger, who in 1930 drenched his fingertips in acid to remove the ridge patterns, failed miserably. His old pattern reappeared as the tips healed.

Fingerprint patterns can change, though. To understand how, let's look at the structure of the skin.

The skin – our largest organ – is divided into two parts:

– a thin almost transparent outer skin, called the epidermis. It walls us from the outside world like a protective shield and houses the ridges and furrows that make fingerprints.

– an inner soft-tissue skin (the dermis), which is filled with nerves, glands, and pipes carrying blood and lymph. The dermis also contains a double row of “pegs,” called the dermal papillae. These “pegs” anchor the outer skin (with its fingerprints) to the inner skin and they create fingerprints.

The double row of “pegs” in the inner skin pokes up and makes fingerprint ridges in the outer skin.

We can envision how the “pegs” make fingerprint ridges that resist change with the help of some clothespins and pink plastic wrap. Imagine setting out a double row of clothespins as the fingerprint “pegs.” Lay a piece of plastic wrap (outer skin) over the double row, poking it down between the clothespin rows. The plastic wrap hits the clothespin tops and forms two parallel ridges – with a furrow in between – much as the skin “pegs” create fingerprint ridges and furrows. See figure.

When the fingertip outer skin gets injured, new cells replace the old. Like laying a new piece of plastic wrap over the clothespin rows, the ridges and furrows remain unchanged because the skin “peg” rows are unchanged. Scarred skin is denser, thicker, and whiter but the ridge patterns look the same.

Damage the “pegs” (dermal papillae) in the inner skin, however, and you can change the double-row layout and, hence, the ridge pattern. Then and only then, the skin grows back with a new fingerprint pattern.

That's what another gangster, Robert Phillips, tried when he had a plastic surgeon remove the skin – outer and inner – from his fingertips and replace it with skin grafts from his chest. To no avail! The FBI simply used prints from his undamaged second joints to identify him.