Tattoos have often been presented in popular media 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 epidermis 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 impossible. 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.
Tetovaže so v popularnih medijih pogosto predstavljene kot znak nevarnih in deviantnih ali kot modna muha mladih. A čeprav različni stili tetovaž pridejo in grejo, in se njihov pomen med kulturami močno razlikuje, je ta praksa stara toliko kot civilizacija sama. Dekorativne okraske na koži so opazili v človeških ostankih po celem svetu, najstarejše so našli na peruvijski mumiji iz leta 6000 pr. n. št. Ampak, ste se kdaj spraševali, kako tetoviranje dejansko poteka? Morda veste, da se koža lušči, izgubimo približno 30-40.000 kožnih celic na uro. To je približno 1.000.000 na dan. Kako torej, da se tetovaža ne olušči postopoma skupaj z njimi? Preprost odgovor je, da tetoviranje prenese pigment globje v kožo, kot je zunanja plast, ki se olušči. Skozi zgodovino so različne kulture uporabljale različne načine tetoviranja. A prva moderna naprava za tetoviranje je bila oblikovana po napravi za graviranje Thomasa Edisona in jo je poganjala elektrika. Moderne naprave za tetoviranje v kožo zapičijo drobne igle, napolnjene z barvo, 50 do 3000-krat na minuto. Igle prodrejo skozi epidermis, da črnilo lahko prodre globoko v dermis, ki je sestavljen iz kolagenskih vlaken, živcev, žlez, krvnih žil in še česa. Vsakič, ko žila prodre v kožo, ustvari rano, ki opozori telo, da naj začne z vnetnim procesom in pokliče celice imunskega sistema na mesto rane, da popravijo kožo. Prav ta proces naredi tetovažo trajno. Kot prvo, specializirane celice, imenovane makrofagi, pojedo tuj material, da bi počistile vnetno zmešnjavo. Ko te celice potujejo skozi limfatični sistem, gredo nekatere s polnim trebuhi barve v bezgavke, medtem ko druge ostanejo v dermisu. Ker barve ne morejo odstraniti, je barvilo v njih vidno skozi kožo. Nekateri delci črnila so prav tako ujeti v gelu podobnem matriksu dermisa, medtem ko druge pogoltnejo dermalne celice imenovane fibroblasti. Sprva je črnilo odloženo tudi v epidermisu, a ko se koža celi, se poškodovane epidermalne celice oluščijo in jih nadomestijo nove celice, brez barvila, najbolj zgornja plast pa se odlušči kot sončna opeklina. Žulji in kraste se pri profesionalnih tetovažah ponavadi ne pojavljajo in popolna obnova epidermisa traja 2-4 tedne, takrat se izogibamo izpostavljenosti soncu in plavanju, da preprečimo bledenje. Dermalne celice pa ostanejo na svojem mestu dokler ne umrejo. Ko umrejo, jih pogoltnejo, skupaj s črnilom, mlade celice blizu njih, zato črnilo ostane, kjer je. A s časom tetovaže zbledijo zaradi odziva telesa na tuje pigmentne delce, ki jih počasi razkraja, da jih lahko odnesejo makrofagi imunskega sistema. Ultravijolično sevanje prav tako prispeva k razkrajanju pigmenta, čeprav lahko to upočasni uporaba zaščite pred soncem. A ker so dermalne celice relativno stabilne, bo večina črnila ostala globoko v koži celo življenje. A če so tetovaže za vedno v vaši koži, jih lahko kako izbrišemo? Načeloma, ja. Danes uporabljamo laser, da prodremo skozi epidermis in razbijemo spodaj ležeče pigmente z različnimi valovnimi dolžinami, pri čemer je črno najlažje naciljati. Laser razgradi skupke črnila v manjše delce, ki jih nato lahko odstranijo makrofagi. A nekatere barve črnila je težje odstraniti kot druge in lahko se pojavijo zapleti. Zato je odstraniti tetovažo težje, kot jo je narediti - a ni nemogoče. Zato morda posamezna tetovaža ne bo v resnici trajala večno, a tetovaže obstajajo dlje kot katerakoli obstoječa kultura. Njihova naraščajoča priljubljenost pomeni, da umetnost tetoviranja ne bo izginila.