Keloid scar

What is a keloid scar?

A keloid scar is a non-cancerous type of change that happens in the skin after an injury. As part of the normal healing response, fibroblasts produce new collagen protein to help rebuild the skin. In some people, fibroblasts make too much collagen. The extra collagen forms a lump that grows beyond the initially injured area. The most common location for a keloid scar is on the upper back, shoulders, chest, and ear lobes. Keloid scars are sometimes referred to only as ‘keloids’.

Skin

Skin is made up of three layers: epidermis, dermis, and subcutaneous fat. The surface and the part you can see when you look at your skin is called the epidermis. The cells that make up the epidermis include squamous cells, basal cells, melanocytes, Merkel cells, and cells of the immune system. The squamous cells in the epidermis produce a material called keratin which makes the skin waterproof and strong and protects us from toxins and injuries.

The dermis is directly below the epidermis. The dermis is separated from the epidermis by a thin layer of tissue called the basement membrane. The dermis contains specialized cells called fibroblasts which produce a type of protein called collagen. Collagen is important because it acts as a glue that helps make the dermis strong and hold the skin together. Below the dermis is a layer of fat called subcutaneous adipose tissue.

What causes a keloid scar?

Doctors do not fully understand why some people develop keloid scars after an injury and others do not. However, keloid scars are more common in people with darker skin. Tension in the skin during wound healing, older age, and wound infection have also been shown to increase the risk of developing a keloid scar.

How do pathologists make this diagnosis?

Pathologists make this diagnosis after a tissue sample from the area is examined under the microscope. Keloid scars are usually much larger than the original site of injury. Pathologists look for broad, uniform, bright pink bundles of collagen in the dermis. Some consider these bundles to look a bit like a rope. The fibroblasts can look a little bigger than normal, and individual fibroblasts can be seen more easily between these bundles. Features associated with cancer are not seen. The epidermis over the keloid scar is typically normal.

by Iris Teo MD FRCPC (updated September 8, 2021)