Tattoos are so hard to remove because they are deposited in the dermis, the lower layer of skin under your epidermis. The introduction of tattoo ink into the dermis triggers an immune response that, ironically, makes the tattoo last longer. There are several ways to remove tattoos, with varying degree of effectiveness.
The upper layer of the skin is called the epidermis. This consists of five layers, from deepest to most superficial: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum. In the top two layers--stratum lucidem and stratum corneum--the skin cells are flattened and dried out, waterproofing and protecting our skin. Skin cells start down in the stratum basale and drift off to the surface, flake off and die within a month; therefore, tattoo ink must penetrate deeper than these layers.
When tattoo ink is deposited in the dermis, below the five epidermal layers, the foreign substance triggers an immune response. The cells in the skin that attack foreign bodies are called phagocytes (phago="eat," cytes="cells"). These "cell eaters" engulf and consume the ink particles. Then fibroblasts (cells that produce collagen) lock the phagocytes together in a network under the skin, just below where the epidermis meets the dermis, about 1 millimeter deep. This enables the tattoo ink to stay in place for many years.
Removal by Abrasion
One of the earliest methods used to tattoo removal, which is sometimes used today, is dermabrasion. This involves "sanding" down the epidermis and some parts of the dermis, rubbing off the tattoo ink. This can also be combined with salabrasion, which uses a salt solution. This method is effective at removing the ink, but leaves a scar in place. Other removal methods include cryosurgery, or freezing the skin, which is followed by excision, or cutting out the skin. If the tattoo is large, a skin graft may be needed to cover the tissues after excision.
Since the 1980s, the most popular way to remove tattoos has been through the use of lasers. This technique is bloodless and usually does not leave scars, but it is time-consuming. Pulses of light are beamed at the skin, which break down the tattoo pigment. This causes a low-grade inflammation, which must heal before more laser work is done. Because of this, treatments are spaced at least six weeks apart, and it can take up to two years to remove a tattoo. This method is most effective on older tattoos (which have already started to break down) and on blue or black ink. It is not effective on yellow or other bright inks, and newer inks are more resistant to breakdown.
Many people choose to have a tattoo covered up by putting another tattoo over it. The old design can be incorporated into the new one, or completely covered by it. There is no such thing as a "removable" or "temporary" tattoo (unless it is painted-on henna or a rub-on transfer), and there is no tattoo ink that degrades over a couple of months.