Abrasion morphology reflects how an object contacts the skin and may preserve features of the causative object.
Brush burns
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Brush burns and friction burns occur in motorcyclists, persons ejected from vehicles, pedestrians and cyclists thrown forward after a motor-vehicle impact.
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A glancing blow with a rough object, such as a stone or stick, can produce a brush burn.
Pressure abrasions
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Pressure abrasions result from crushing of the superficial epidermal layers and are associated with bruising of the surrounding area.
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The instrument moves approximately perpendicular to the skin, with slight movement directed largely inwards.
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Examples include ligature marks in hanging and strangulation and teethbite marks.
Impact abrasions
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Impact, contact or imprint abrasions result from impact with a rough object when force acts at or near a right angle to the skin.
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The abrasion is slightly depressed unless underlying contusion or local oedema causes bulging. A forcible impact can damage the dermis and produce an underlying bruise.
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A vehicle impact may leave a radiator-grille, headlamp-rim or tyre-tread pattern. Road dirt, paint flakes or grease may be present.
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A solid object may produce peripheral abrasion where the skin is forced downwards. Contact with a flat, relatively smooth surface may produce an abrasion with little or no linear marking.
Patterned abrasions
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Impact and pressure abrasions that reproduce the causative object's pattern are called patterned abrasions.
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A patterned injury suggests the inflicting instrument or a distinctive means of causation. Patterned abrasions are produced by force applied at a right angle to the skin.