Mysterious circle tattoos on a Peruvian mummy contained burned plant material-a feat that sheds light on a possible ancient healing practice that may have been based on similar principles to acupuncture.
The 1000-year-old female mummy was found unwrapped in the sand of the desert at Chiribaya Alta in southern Peru in the early 1990s and bears two tattoos on the body.
One of them is a tattoo of an asymmetric pattern of overlapping circles on her neck.
Maria Anna Pabst of the Medical University of Graz in Austria and her colleagues used microscopy and spectroscopy to analyse the tattoos.
Almost all known ancient tattoos were made with ash or soot. But the researchers found that while this was true for the tattoos on this mummy's extremities, the circles on her neck contained burned plant material.
"If you use different materials, they have different functions," New Scientist quoted her as saying.
The team believe that while the soot tattoos were decorative, the neck circles were probably part of a healing or strengthening ritual.
Pabst points out that the circles are close to Chinese acupuncture points. She says that tattooing a person at these points could have worked in a similar way to how acupuncture is thought to work.
The idea that some ancient tattoos have a therapeutic purpose has been suggested before but Pabst's study is the first to compare the two types of tattoo in the same mummy.