About the skin
The skin is the largest organ. It protects the body against infection and injury and helps regulate body temperature. The skin also stores water and fat and produces vitamin D.
The skin is made up of three main layers:
The epidermis. The outer layer of skin.
The dermis. The inner layer of skin.
The hypodermis. The deep layer of fat.
See the Medical Illustrations section for a drawing of these layers.
About skin cancer
Cancer begins when healthy cells change and grow uncontrollably, forming a mass called a tumor. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can grow and spread to other parts of the body. A benign tumor means the tumor can grow but will not spread.
Doctors diagnose more than two million Americans with skin cancer each year, making it the most common type of cancer. If skin cancer is found early, it can usually be cured with a relatively simple surgery. As a result, skin cancer is responsible for less than 1% of all cancer deaths.
Types of skin cancer
There are three main types of skin cancer:
Basal cell carcinoma. Basal cells are the round cells found in the lower epidermis. About 80% of skin cancers develop from this type of cell. These cancers are described as basal cell carcinomas. Basal cell carcinoma most often develops on the head and neck. It is mainly caused by sun exposure or develops in people who received radiation therapy as children. This type of skin cancer usually grows slowly and rarely spreads to other parts of the body.
Squamous cell carcinoma. Most of the epidermis is made up of flat, scale-like cells called squamous cells. Approximately 20% of skin cancers develop from these cells, and these cancers are called squamous cell carcinomas. Squamous cell carcinoma is mainly caused by sun exposure, but it can develop on skin that has been burned, damaged by chemicals, or exposed to x-rays. Other areas where squamous cell carcinoma is commonly found include the lips; sites of a chronic inflammatory skin condition; and skin outside the mouth, anus, and a woman’s vagina. Squamous cell carcinoma rarely spreads to other parts of the body, but it is more likely to spread than basal cell carcinoma.
Melanoma. Where the epidermis meets the dermis, there are scattered cells called melanocytes. These cells produce the pigment melanin that gives skin color. Melanoma starts in melanocytes, and it is the most serious type of skin cancer. For more information about melanoma, please visit the melanoma section.
Basal cell carcinoma and squamous cell carcinoma are generally grouped together and called “non-melanoma skin cancer” to distinguish them from melanoma. Melanoma develops from very different cells and is treated differently because it is more likely to spread than other skin cancers. Typically, non-melanoma skin cancer can be treated with a relatively simple surgery. If the cancer is very small, medicated creams prescribed by a doctor, cauterization (burning), cryosurgery (freezing), or laser surgery may be used. Learn more in the Treatment Options section.
There are a few other rarer types of skin cancer, including keratoacanthomas, Merkel cell carcinoma, cutaneous (skin) lymphomas, Kaposi sarcoma, skin adnexal tumors, and sarcomas, all of which are classified as non-melanoma skin cancers. However, this section focuses on basal cell and squamous cell skin cancers.
Normal Skin TissueClick to Enlarge
Basal cell carcinomaClick to Enlarge
Squamous cell carcinomaClick to Enlarge
These images used with permission by the College of American Pathologists.
Looking for More of an Overview?
If you would like additional introductory information, explore this related item. Please note this link will take you to another section on Cancer.Net:
- ASCO Answers Fact Sheet: Read a one-page fact sheet (available as a PDF) that offers an easy-to-print introduction to basal cell carcinoma.