The dermis is the thick middle layer of the skin. It sits under the epidermis, the thin outer layer, and above the fat under the skin. The dermis gives the skin its strength and flexibility, and it contains the blood vessels, nerves, hair follicles, and glands that support the skin.
The dermis is a normal part of the skin, not a diagnosis. It is mentioned in many skin pathology reports to describe where a finding is located. This article explains what the dermis is made of, what it looks like under the microscope, and why its name appears in your pathology report.
What are the layers of the skin?
The skin is made of three main layers. From the surface down, they are:
- Epidermis. The thin outer layer, made mostly of squamous cells. It forms a protective barrier and contains the pigment cells called melanocytes.
- Dermis. The thicker middle layer, made mostly of tough fibers. It supports the epidermis and supplies it with blood and nerves.
- Subcutaneous tissue. The deepest layer, made mostly of fat, also called adipose tissue. It cushions the body and stores energy.
The dermis varies in thickness across the body. It is very thin on the eyelids and much thicker on the back.
What is the dermis made of?
Most of the dermis is made of collagen, a strong protein that gives the skin its strength. Elastic fibers mixed in with the collagen allow the skin to stretch and spring back. These fibers are made by cells called fibroblasts.
The dermis also contains:
- Blood vessels and lymphatic vessels. These bring nutrients to the skin and carry away fluid and waste.
- Nerves. These allow the skin to sense touch, pain, and temperature.
- Hair follicles and glands. These include sebaceous glands, which make oil, and sweat glands.
- Immune cells. Cells such as macrophages help protect the skin from infection.
What does the dermis look like under the microscope?
Under the microscope, the dermis appears as a pink layer of fibers below the darker, cell-rich epidermis. Pathologists divide it into two parts:
- Papillary dermis. The thin upper part, directly under the epidermis. It contains fine, loosely arranged fibers and small blood vessels.
- Reticular dermis. The thicker lower part. It contains thick bundles of collagen, along with most of the hair follicles and glands.
In skin with significant sun exposure, the fibers in the upper dermis can become thick and tangled. This change is called solar elastosis.
Why is the dermis mentioned in a pathology report?
Pathology reports often describe where a finding is located in the skin. The dermis is mentioned for several reasons:
- To show whether a cancer is invasive. Some skin cancers begin in the epidermis. When the cancer cells stay in the epidermis, the cancer is described as in situ. When they grow down into the dermis, the cancer is described as invasive. For example, squamous cell carcinoma in situ is confined to the epidermis, while invasive squamous cell carcinoma has spread into the dermis.
- To measure the depth of melanoma. In invasive melanoma, the pathologist measures how far the tumor extends into the dermis. This measurement is called the Breslow thickness. It is one of the most important features of melanoma. Older reports may also include the Clark level.
- To describe where a mole is located. Moles are named by where the mole cells sit. A dermal nevus is found in the dermis. A compound nevus is found in both the epidermis and the dermis.
- To describe tumors that start in the dermis. Some tumors grow from the cells of the dermis itself. Examples include a dermatofibroma and dermatofibrosarcoma protuberans.
- To describe the deep margin. The deep margin is the bottom edge of the removed skin. Your report may say whether a tumor extends to the deep dermis or reaches the deep margin.
Questions to ask your doctor
- Which layer of my skin was involved?
- Did the tumor grow into the dermis?
- Is my cancer in situ or invasive?
- How deep into the dermis did the tumor extend?
- Was the deep margin free of tumor?
- Does the depth of the tumor change my treatment?
- Do I need any further surgery or follow-up?
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