'Pigments from tattoos travel to the lymph nodes'
The researchers used powerful X-rays to identify titanium dioxide and heavy metals present in tattooed skin and lymph node tissue samples.
Although particles of varying sizes are found in the skin, only highly microscopic titanium dioxide fragments are present in the nodes, which may cause them to become swollen.
The researchers believe the particles may be transported in the blood or engulfed by immune cells that subsequently deposit them.
This deposition may cause lymph nodes to swell, impairing their ability to fight infections and filter out pathogens.
Study author Bernhard Hesse said: "We already knew that pigments from tattoos would travel to the lymph nodes because of visual evidence: the lymph nodes become tinted with the colour of the tattoo. It is the response of the body to clean the site of entrance of the tattoo.
"What we didn't know is that they do it in a nano form, which implies that they may not have the same behaviour as the particles at a micro level. And that is the problem: we don't know how nanoparticles react.
The findings were published in the journal Scientific Reports.
What is titanium dioxide?
Titanium dioxide is the second most commonly used ingredient in tattoo ink.
Its whitening and thickening properties means it is also added to washing detergents, fragrances, air fresheners and paint, as well as being used in cooling liquids in fridges and as a lubricant in motor oil.
On June 9 2017, the European Chemicals Agency announced titanium dioxide is a substance suspected of causing cancer when inhaled.
Previous research has linked titanium dioxide to itching and delayed healing.