Following a cut or wound on the skin, keloids develop within the scar tissue. As the body attempts to repair the wound, the collagen overgrows, sometimes producing a large lump. Type III collagen, also known as granulation tissue, occurs in the earlier keloids, while type I occurs in the later forms. Piercings, severe acne, chickenpox scarring, infections, burns, vaccinations, repeated trauma to the skin or tension during wound closure can also be known to cause them; something as simple as a pimple, insect bite or scratch can, too. In terms of locations on the body, the most common areas include the chest, back, shoulders, earlobes, arms, pelvic region and the collarbone. The general theme is a predilection for areas of the body where the skin is under tension (stretched as in e.g. chest, collar bones) or pulling effect of gravity (e.g. an earlobe that is pulled down by a heavy earring after piercing). Although an injury is usually responsible for this type of scarring, keloids can occur spontaneously. They are also prone to growth, especially if they first appear at a younger age.