Keloid - Causes and Diagnosis

What causes a keloid scar to form?

Science hasn't yet managed to explain why some people go on to develop keloid scars after their skin is damaged, and others don't. But we have a pretty good idea of how it happens.

Keloid scars form because the normal process of scarring, that we all have, goes into overdrive:

  • Normally when the skin is damaged, fresh skin is laid down to heal the damage but then the damaged area you see gradually fades away (the medical term for this process is 'involution').
  • In a keloid scar too much collagen is laid down in the skin after the damage has happened. It heals 'too much'.
  • Then, instead of simply fading away, the scar tissue just stays where it is.
  • The people who get keloid scars are usually those who have black skin and who originate from Africa or the Caribbean.
  • No one quite knows why this happens. It seems to be unique to humans: other animals do not get keloid scars.

How does a doctor diagnose a keloid scar?

  • There is no particular test for a keloid scar. It is diagnosed from the clinical story (a slow-growing overgrowth of a scar, usually in a dark-skinned person), with the scar growing beyond the location of the original skin damage.
  • Occasionally a keloid scar can mimic other skin tumours.
  • Very rarely, a skin tumour like a dermatofibroma or a soft tissue sarcoma can be mistaken for a keloid scar, or vice versa.
  • In that case, a biopsy will need to be taken by a specialist. A biopsy is a procedure where a sample of tissue is taken for further analysis.
  • The biopsy will be looked at under a microscope and a specialist (histopathologist) will be able to see the typical microscopic features of a keloid scar: a swirling nodular pattern of collagen fibres.
  • Note: a biopsy is hardly ever necessary because the history - ie the patient's story - and the appearance of the skin growth are very typical of a keloid scar.

What do keloid scars look like?

This image shows a keloid scar on a 4-year-old child's toes, that formed following surgery he had at the age of 2 years:

Keloid on toes of a child after surgery. free image from

The image below shows a keloid scar on a woman's ear, after an ear piercing.

Keloid of ear auricle (not ear lobe).
Free image from

Images from Openi® (Open Access Biomedical Image Search Engine)  

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Dr Oliver Starr
Peer Reviewer:
Dr Laurence Knott
Document ID:
13624 (v3)
Last Checked:
11 May 2017
Next Review:
29 June 2020

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. Patient Platform Limited has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.