A close-up clinical image can sometimes leave people wondering what they are looking at—and this one is particularly striking. The photograph shows a person’s upper back while a healthcare professional uses sterile instruments to carefully examine and remove a dark, compact mass from the skin.

The appearance may resemble a large blackhead or a hardened skin plug, but there are several conditions that can produce similar-looking material. A photograph alone cannot establish the exact diagnosis.

What Is That Dark Material?

The material appears to be a dense keratinous or sebum-containing plug surrounded by a localized area of irritated skin.

Keratin is a protein naturally produced by the skin. When dead skin cells, oil, and keratin become trapped inside a follicle or enlarged opening, they can gradually form a compact plug.

When the opening is exposed to air, the surface material can become dark through oxidation. This is one reason some clogged pores appear almost black.

However, a larger or unusually shaped lesion should not automatically be assumed to be an ordinary blackhead.

Why Can a Plug Become So Large?

Several different skin problems can create a similar appearance.

Possible causes may include:

• Large open comedones
• Epidermoid cysts
• Dilated or enlarged pores
• Accumulated keratin
• Blocked hair follicles
• Certain localized follicular disorders

An epidermoid cyst, for example, can contain a thick, whitish-to-yellow keratin material and may develop a visible opening called a punctum. Other lesions can also become filled with keratin and appear dark after prolonged exposure.