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This activity was written by our awesome past forensic science camp director, Jess. Even though she's off to grad school now, Jess wanted to leave you with this cool activity to do at home!

Did you know that no one else in the world has the same fingerprints as you? At first glance, your fingerprints may look similar to your siblings’, your parents’, or your friends’. But if you look more closely, you’ll see there are many small details that set them apart! Not even identical twins’ fingerprints are exactly the same.

Since they are unique, fingerprints can be very useful to crime scene investigators and forensic scientists. If investigators find a fingerprint at a crime scene, they will compare it with a suspect’s fingerprints to find out if they were at the scene. Your fingertips have ridges and furrows. The ridges are like little hills, and the furrows are valleys. When you leave a fingerprint behind, you are looking at the ridges. Scientists look at the overall ridge pattern and minutiae when examining a fingerprint.

There are three overall patterns: arches, loops, and whorls. Arches look like tents, arches, or spikes. The ridges come in from one side of the fingerprint, rise up, then go back down and exit the other side of the print. For loops, the ridges enter one side of the print, loop around, and exit out the same side. Even if there is only one ridge that makes a loop, that’s enough for the whole fingerprint to be considered a loop! Finally, there are whorls. Whorls look like a bullseye or a spiral. Loops are the most common, followed by whorls. Arches are quite rare! But don’t worry, even if all your fingerprints are loops, they are still unique, thanks to their minutiae.

 Minutiae are the little tiny details that make your fingerprints special. There are many types of minutiae, such as islands and enclosures, trifurcations and double bifurcations, bridges and spurs (oh my!)… but they are all combinations of ridge endings (where a ridge stops or starts) and bifurcations (where a ridge splits into two). It is the type and relative location of the minutiae that makes each fingerprint unique. When forensic scientists compare two fingerprints, they look to see if they have the same minutiae in the same location. If even one minutia is missing or different, the scientist knows they are not from the same finger.

Forensic scientists use magnifying glasses and computer programs to look at fingerprints. But there’s an easy way to look at your fingerprints using something you might have at home- a balloon! You will also need ink, either from an ink pad or a marker. Dark colors are best, since the print will become lighter after you blow up the balloon. Make sure the ink is washable, otherwise you’ll have colored fingertips for a few days! First, make a few test fingerprints on a piece of paper, to get the hang of how much ink to use. Then, make a fingerprint on the balloon. Make sure the balloon is uninflated and as flat as possible when you make the print. Once the fingerprint is dry, blow up the balloon. As the balloon expands, your fingerprint will expand with it! What type of overall pattern do you have- an arch, a loop, or a whorl? Can you see any minutiae? You may notice some other features. Do you see some circles within the ridges? These are pores you have in your fingertips that produce sweat. Do you have a scar on your fingertip? You will see that in your fingerprint too!