Why Tattoos Don't "Heal"
Professional tattoos are created by rapidly puncturing the skin to inject droplets of ink into the dermis of your skin. Because the ink goes into the dermis and not the epidermis, which is constantly sloughing off skin cells, the pattern created by the ink is permanent and will maintain its shape, though stretching and fading do occur over time.
How Skin Heals
When your skin gets cut, your body springs into action to heal the wound. First, the body works to limit blood loss by reducing the amount of blood flowing to the wounded area. Proteins in blood, such as fibrin, work with the blood platelets already in place and plasma to form a protective covering called a scab. While your skin regenerates underneath the protective layer, the scab protects the wound from outside infection.
The wound is gradually healed as new granular skin tissue begins to generate. Starting at the edges of the wound, the new tissue forms and works its way toward the center until it has covered the entirety of the lesion. Once the wound underneath has sealed itself with another skin layer, the scab will slough off on its own.
If the cut or scrape was a shallow one that only affected the outer epidermis layer, then there shouldn't be a scar when your skin heals itself. If the cut went deeper, into the dermis of the skin, then cicatrisation begins as your body moves to create fibrous scar tissue from the granular tissue. In general, the worse the wound, the greater chance that it will result in a scar. Your body needs three to six weeks to bridge a deep cut, producing a protein called collagen at the site of the wound to repair it. Even after the wound is healed, it can take up to two years for a scar to settle into its permanent appearance [source: Ditkoff].
Scar skin tissue isn't like normal skin tissue -- it doesn't have sweat glands or hair growing from it. It's also more vulnerable to ultraviolet rays. Most scars are whitish and lay flat on the surface of your skin. But some scars, such as hypertrophic scars and keloids, take on an odd appearance. Hypertrophic scars are raised at the site of the original wound, reddish and sometimes itchy. Over time, they can subside. Keloid scars are also raised and red, but they grow past the site of the wound, overtaking normal healthy tissue. Researchers haven't yet been able to determine what causes these abnormal scars to form, but one theory is that they may be caused by changes to the signals sent by cells at the wound site. It seems these cells continue to direct the body to produce more fibrous tissue even after the wound has closed [source: Rockoff]. Laser treatments and cortisone injections are two methods used to treat keloids.
Scars, of course, aren't the only feature marking adult skin that was once baby-smooth. On the next page, find out how skin ages.