as either marks of the dangerous and deviant

or trendy youth fads.

But while tattoo styles come and go,

and their meaning has differed greatly across cultures,

the practice is as old as civilization itself.

Decorative skin markings have been discovered in human remains

all over the world,

with the oldest found on a Peruvian mummy dating back to 6,000 BCE.

But have you ever wondered how tattooing really works?

You may know that we shed our skin,

losing about 30-40,000 skin cells per hour.

That's about 1,000,000 per day.

So, how come the tattoo doesn't gradually flake off along with them?

The simple answer is that tattooing involves getting pigment deeper into the skin

than the outermost layer that gets shed.

Throughout history, different cultures have used various methods to accomplish this.

But the first modern tattooing machine

was modeled after Thomas Edison's engraving machine

and ran on electricity.

Tattooing machines used today

insert tiny needles, loaded with dye, into the skin

at a frequency of 50 to 3,000 times per minute.

The needles punch through the epidermis,

allowing ink to seep deep into the dermis,

which is composed of collagen fibers, nerves, glands, blood vessels and more.

Every time a needle penetrates, it causes a wound

that alerts the body to begin the inflammatory process,

calling immune system cells to the wound site to begin repairing the skin.

And it is this very process that makes tattoos permanent.

First, specialized cells called macrophages

eat the invading material in an attempt to clean up the inflammatory mess.

As these cells travel through the lymphatic system,

some of them are carried back with a belly full of dye into the lymph nodes

while others remain in the dermis.

With no way to dispose of the pigment,

the dyes inside them remain visible through the skin.

Some of the ink particles are also suspended in the gel-like matrix of the dermis,

while others are engulfed by dermal cells called fibroblasts.

Initially, ink is deposited into the eipdermis as well,

but as the skin heals, the damaged epidermal cells are shed

and replaced by new, dye-free cells

with the topmost layer peeling off like a heeling sunburn.

Blistering or crusting is not typically seen with professional tattoos

and complete epidermal regeneration requires 2-4 weeks

during which excess sun exposure and swimming should be avoided to prevent fading.

Dermal cells, however, remain in place until they die.

When they do, they are taken up, ink and all, by younger cells nearby

so the ink stays where it is.

But with time, tattoos do fade naturally as the body reacts to the alien pigment particles,

slowly breaking them down to be carried off by the immune system's macrophages.

Ultraviolet radiation can also contribute to this pigment breakdown,

though it can be mitigated by the use of sunblock.

But since the dermal cells are relatively stable,

much of the ink will remain deep in the skin for a person's whole life.

But if tattoos are embedded in your skin for life, is there any way to erase them?

Technically, yes.

Today, a laser is used to penetrate the epidermis

and blast apart underlying pigment colors of various wavelengths,

black being the easiest to target.

The laser beam breaks the ink globules into smaller particles

that can then be cleared away by the macrophages.

But some color inks are harder to remove than others,

and there could be complications.

For this reason, removing a tattoo is still more difficult than getting one --

but not impossbile.

So a single tattoo may not truly last forever,

but tattoos have been around longer than any existing culture.

And their continuing popularity means that the art of tattooing is here to stay.