A scar is a mark left on the skin after a wound or injury has healed.
Scars are a natural part of the healing process. Most will fade and become paler over time, although they never completely disappear.
A scar can be a fine line or a pitted hole on the skin, or an abnormal overgrowth of tissue.
A minor wound like a cut will usually heal to leave a red, raised line, which will gradually get paler and flatter over time.
This process can take up to two years. The scar won't disappear completely and you'll be left with a visible mark or line.
Fine-line scars are common following a wound or after surgery. They aren't usually painful, but they may be itchy for a few months.
On darker skin types, the scar tissue may fade to leave a brown or white mark. A pale scar may be more obvious on tanned skin because scar tissue doesn't tan.
A keloid scar is an overgrowth of tissue that occurs when too much collagen is produced at the site of the wound.
The scar keeps growing, even after the wound has healed.
Keloid scars are raised above the skin and are red or purple when newly formed, before gradually becoming paler. They're often itchy or painful, and can restrict movement if they're tight and near a joint.
Like keloid scars, hypertrophic scars are the result of excess collagen being produced at the site of a wound.
But not as much collagen is produced in hypertrophic scars compared with keloid scars.
Also, unlike keloid scars, hypertrophic scars don't extend beyond the boundary of the original wound, but they may continue to thicken for up to six months.
Hypertrophic scars are red and raised to start with, before becoming flatter and paler over the course of several years.
Pitted scars, also known as atrophic or "ice-pick" scars, can also occur as a result of an injury that causes a loss of underlying fat.
Scar contractures are often caused by burns.
They occur when the skin "shrinks", leading to tightness and a restriction in movement.
Complete scar removal isn't possible, but most scars will gradually fade and become paler over time.
A number of treatments are available that may improve a scar's appearance and help make it less visible.
If scarring is unsightly, uncomfortable or restrictive, treatment options may include:
In many cases, a combination of treatments can be used.
Read more about treating scars.
Scarring can affect you both physically and psychologically.
A scar, particularly if it's on your face, can be very distressing. The situation can be made worse if you feel you're being stared at.
If you avoid meeting people because of your appearance, it's easy to become socially isolated. This can lead to feelings of depression.
See your GP if you feel your scars are making you depressed, or if they're affecting your daily activities.
A number of support groups and organisations provide help and advice for people living with scarring.
Scarring is part of the body's natural healing process after tissue is damaged.
When the skin is wounded, the tissues break, which causes a protein called collagen to be released. Collagen builds up where the tissue is damaged, helping to heal and strengthen the wound.
New collagen continues forming for several months and the blood supply increases, causing the scar to become red, raised and lumpy.
In time, some collagen breaks down at the site of the wound and the blood supply reduces. The scar gradually becomes smoother, softer and paler.
Although scars are permanent, they can fade over a period of up to two years. It's unlikely they'll fade any more after this time.
Stretch marks are narrow streaks or lines that appear on the skin's surface when the deeper layer of skin (dermis) tears.