Tattoos have often been presented in popular media as either marks of the dangerous and deviant or trendy youth fads.
纹身，在大众媒体中经常被当作危险和怪异的标志，或者是时髦的年轻风尚。
But while tattoo styles come and go,
但是尽管流行的纹身图案经常变换，
and their meaning has differed greatly across cultures, the practice is as old as civilization itself.
在不同文化环境中代表的含义也差别巨大，但纹身这种行为却像人类的文明本身一样古老。
Decorative skin markings have been discovered in human remains all over the world,
装饰性的皮肤标记在世界各地的人类遗迹中都有发现，
with the oldest found on a Peruvian mummy dating back to 6,000 BCE.
其中最古老的是公元前6000年的秘鲁木乃伊。
But have you ever wondered how tattooing really works?
但你是否好奇过纹身的原理到底是什么？
You may know that we shed our skin, losing about 30-40,000 skin cells per hour.
你或许知道，我们也会脱皮，每个小时会代谢掉3到4万个皮肤细胞。
That's about 1,000,000 per day. So, how come the tattoo doesn't gradually flake off along with them?
一天大约是1百万个皮肤细胞。那么，纹身怎么没有随着皮肤细胞的代谢而剥落呢？
The simple answer is that tattooing involves getting pigment deeper into the skin than the outermost layer that gets shed.
简单的回答是，纹身的过程是把颜料植入外层可以脱落的皮肤之下。
Throughout history, different cultures have used various methods to accomplish this.
纵观历史，不同的文化有不同的纹身方法。
But the first modern tattooing machine was modeled after Thomas Edison's engraving machine and ran on electricity.
但是第一台现代纹身机器脱胎于托马斯·爱迪生发明的雕刻机，靠电力运行。
Tattooing machines used today insert tiny needles, loaded with dye, into the skin at a frequency of 50 to 3,000 times per minute.
今天所使用的纹身机是把沾有颜料的细针刺入皮肤，以每分钟50到3000次的频率震动。
The needles punch through the epidermis, allowing ink to seep deep into the dermis,
细针刺透表皮，让颜料深入真皮，
which is composed of collagen fibers, nerves, glands, blood vessels and more.
真皮之下是胶原纤维、神经、腺体、血管等等。
Every time a needle penetrates, it causes a wound that alerts the body to begin the inflammatory process,
针的每一下刺入，都会造成伤口，身体会立即开始对抗炎症的反应，
calling immune system cells to the wound site to begin repairing the skin.
召唤免疫细胞到伤口处修复皮肤。
And it is this very process that makes tattoos permanent.
就是在这个过程中，纹身图案得以永久保留。
First, specialized cells called macrophages eat the invading material in an attempt to clean up the inflammatory mess.
首先，巨噬细胞会吃掉外来物质，试图清理有可能出现的炎症。
As these cells travel through the lymphatic system,
当这些细胞在淋巴系统中运动，
some of them are carried back with a belly full of dye into the lymph nodes while others remain in the dermis.
有一部分携带着大量颜料进入淋巴结，另外一些依然留在表皮之下。

With no way to dispose of the pigment, the dyes inside them remain visible through the skin.
由于再没有其它方式去除颜料，细胞中的颜料因此在皮肤下面清晰可见。
Some of the ink particles are also suspended in the gel-like matrix of the dermis,
有些颜料颗粒悬浮在胶质的真皮结构中，
while others are engulfed by dermal cells called fibroblasts.
而其它颜料颗粒被叫做成纤维细胞的真皮细胞吞噬。
Initially, ink is deposited into the epidermis as well,
最初，纹身的过程也会把颜料植入表皮，
but as the skin heals, the damaged epidermal cells are shed
但是随着皮肤的自我修复，损坏的表皮细胞脱落，
and replaced by new, dye-free cells with the topmost layer peeling off like a heeling sunburn.
被新的、没有颜料的细胞所替代，如同表层皮肤被阳光灼伤一样脱落。
Blistering or crusting is not typically seen with professional tattoos and complete epidermal regeneration requires 2-4 weeks,
专业的纹身过程不大会出现肿胀和结痂的现象，完整的表皮自我修复需要2到4周，
during which excess sun exposure and swimming should be avoided to prevent fading.
在此期间应当尽量避免过度日照和游泳，以防止纹身褪色。
Dermal cells, however, remain in place until they die.
真皮细胞依然存在，直到死去。
When they do, they are taken up, ink and all, by younger cells nearby, so the ink stays where it is.
死去之后，它们体内的颜料被附近新生的细胞所携带，所以颜料不会被代谢出体外。
But with time, tattoos do fade naturally as the body reacts to the alien pigment particles,
但随着时间推移, 纹身的确会自然褪色，因为身体会对外来的色素颗粒产生反应，
slowly breaking them down to be carried off by the immune system's macrophages.
缓慢地将其分解，由免疫系统的巨噬细胞带出体外。
Ultraviolet radiation can also contribute to this pigment breakdown, though it can be mitigated by the use of sunblock.
紫外线照射也可以加速颜料的分解，当然，防晒霜可以起到一些保护作用。
But since the dermal cells are relatively stable, much of the ink will remain deep in the skin for a person's whole life.
但由于真皮细胞相对稳定，大部分颜料会伴随人的一生，存在于皮肤之下。
But if tattoos are embedded in your skin for life, is there any way to erase them? Technically, yes.
但是如果纹身将会伴你一生，那么有没有办法将其擦除？从技术角度讲是有的。
Today, a laser is used to penetrate the epidermis
今天，可以用激光来穿透表皮，
and blast apart underlying pigment colors of various wavelengths, black being the easiest to target.
分解掉隐藏在内部的、具有不同波长的颜料颗粒，黑色最容易被分解。
The laser beam breaks the ink globules into smaller particles that can then be cleared away by the macrophages.
激光把颜料块击碎，变成更小的颗粒，巨噬细胞可以将其清除。
But some color inks are harder to remove than others, and there could be complications.
但是有些颜色很难消除，而且会出现并发症。
For this reason, removing a tattoo is still more difficult than getting one, but not impossible.
所以擦除纹身依然比刺上纹身难很多，但也并非绝无可能。
So a single tattoo may not truly last forever, but tattoos have been around longer than any existing culture.
所以一个纹身不一定会伴你一生，但纹身的存在远比任何一种现存的文化更加古老。
And their continuing popularity means that the art of tattooing is here to stay.
而且人们对其的热衷，会让这种艺术继续存在下去。