Scars develop as a result of tissue damage such as trauma, burns, surgery, acne or infection. This damaged tissue is repaired and replaced with new collagen. This collagen appears as a scar. New scars are red (erythematous) and as they mature the scars become paler and white or, on occasion pigmented. If there is too much collagen then the scar appears as a hard nodule and is called a hypertrophic or keloid scar. If there is too little collagen then the scar appears as a depression or indented area and is called an atrophic scar.
In summary therefore a scar can be described by its colour, its collagen content and its surface profile: