Unlike tattoos which are permanent for an entire lifetime, semi-permanent makeup uses tiny particles of pigment beneath the surface of the skin, much like a tattoo but which will only stay in the skin for a number of years. Therefore it can be naturally erased after a number of years.
As the natural pigment is applied between the skin surface and epidermis layer it causes almost no allergic reactions or discoloration, and also has an advantage that it can be repeated to update the look in according to the latest trends.