Here's why tattoos stay in your skin forever

• The reason tattoo ink stays in skin forever has to do with the immune system.  
• When you get a tattoo, the ink flows down the tattooing needle into the middle layer of your skin, called the dermis.
• That creates a wound, which your body tries to heal by sending macrophages (a type of white blood cell) to the area.
• The macrophages swallow the ink in an effort to take the foreign particle away from the wound.
• But the pigment in the ink is too large for the macrophages to remove, so the macrophages - with the ink inside - end up stuck in the dermis. 

NOW WATCH: Here's why I'm donating my body to science