What are basal and squamous cell skin cancers?

To understand basal and squamous cell skin cancers, it helps to know about the normal 
structure and function of the skin.  
Normal skin 
The skin is the largest organ in your body. It does several different things: 
• Covers the internal organs and protects them from injury 
• Serves as a barrier to germs such as bacteria 
• Prevents the loss of too much water and other fluids 
• Helps control body temperature 
• Protects the rest of the body from ultraviolet (UV) rays 
• Helps the body make vitamin D 
The skin has 3 layers: the epidermis, the dermis, and the subcutis (see picture). 
Epidermis 
The top layer of skin is the epidermis. The epidermis is thin, averaging only 0.2 
millimeters thick (about 1/100 of an inch). It protects the deeper layers of skin and the 
organs of the body from the environment.

Keratinocytes are the main cell type of the epidermis. These cells make an important 
protein called keratin. Keratin helps the skin protect the rest of the body.  
The outermost part of the epidermis is called the stratum corneum, or horny layer. It is 
composed of dead keratinocytes that are continually shed as new ones form. The cells in 
this layer are called squamous cells because of their flat shape. 
Living squamous cells are found just below the stratum corneum. These cells have moved 
here from the lowest part of the epidermis, the basal layer. The cells of the basal layer, 
called basal cells, continually divide to form new keratinocytes. These replace the older 
keratinocytes that wear off the skin's surface.  
Cells called melanocytes are also found in the epidermis. These skin cells make the 
brown pigment called melanin. Melanin is what gives the skin its tan or brown color. It 
protects the deeper layers of the skin from some of the harmful effects of the sun. When 
skin is exposed to the sun, melanocytes make more of the pigment, causing the skin to tan 
or darken. 
The epidermis is separated from the deeper layers of skin by the basement membrane. 
The basement membrane is an important structure because when a skin cancer becomes 
more advanced, it generally grows through this barrier. 
Dermis 
The middle layer of the skin is called the dermis. The dermis is much thicker than the 
epidermis. It contains hair follicles, sweat glands, blood vessels, and nerves that are held 
in place by a protein called collagen. Collagen, made by cells called fibroblasts, gives the 
skin its resilience and strength. 



Subcutis 
The deepest layer of the skin is called the subcutis. The subcutis and the lowest part of 
the dermis form a network of collagen and fat cells. The subcutis helps the body conserve 
heat and has a shock-absorbing effect that helps protect the body's organs from injury. 
Types of skin cancer 
Melanomas 
Cancers that develop from melanocytes, the pigment-making cells of the skin, are called 
melanomas. Melanocytes can also form benign growths called moles. Melanoma and 
moles are discussed in our document called Melanoma Skin Cancer.  
Skin cancers that are not melanoma are sometimes grouped together as non-melanoma 
skin cancers because they tend to act very differently from melanomas. 
Keratinocyte cancers  
These are by far the most common non-melanoma skin cancers. They are called 
keratinocyte carcinomas or keratinocyte cancers because when seen under a microscope, 
their cells share some features of keratinocytes, the most abundant cell type of normal 
skin. The most common types of keratinocyte cancer are basal cell carcinoma and 
squamous cell carcinoma.  

Subcutis 
The deepest layer of the skin is called the subcutis. The subcutis and the lowest part of 
the dermis form a network of collagen and fat cells. The subcutis helps the body conserve 
heat and has a shock-absorbing effect that helps protect the body's organs from injury. 
Types of skin cancer 
Melanomas 
Cancers that develop from melanocytes, the pigment-making cells of the skin, are called 
melanomas. Melanocytes can also form benign growths called moles. Melanoma and 
moles are discussed in our document called Melanoma Skin Cancer.  
Skin cancers that are not melanoma are sometimes grouped together as non-melanoma 
skin cancers because they tend to act very differently from melanomas. 
Keratinocyte cancers  
These are by far the most common non-melanoma skin cancers. They are called 
keratinocyte carcinomas or keratinocyte cancers because when seen under a microscope, 
their cells share some features of keratinocytes, the most abundant cell type of normal 
skin. The most common types of keratinocyte cancer are basal cell carcinoma and 
squamous cell carcinoma.  
Basal cell carcinoma 
When seen under a microscope, these cancers share features with the cells in the lowest 
layer of the epidermis, called the basal cell layer.  
About 8 out of 10 skin cancers are basal cell carcinomas (also called basal cell cancers). 
They usually develop on sun-exposed areas, especially the head and neck. Basal cell 
carcinoma was once found almost exclusively in middle-aged or older people. Now it is 
also being seen in younger people, probably because they are spending more time in the 
sun with their skin exposed.  
Basal cell carcinoma tends to be slow growing. It is very rare for a basal cell cancer to 
spread to nearby lymph nodes or to distant parts of the body. But if a basal cell cancer is 
left untreated, it can grow into nearby areas and invade the bone or other tissues beneath 
the skin.  
After treatment, basal cell carcinoma can recur (come back) in the same place on the 
skin. People who have had basal cell cancers are also more likely t

When seen under a microscope, these cancers share features with the cells in the lowest 
layer of the epidermis, called the basal cell layer.  
About 8 out of 10 skin cancers are basal cell carcinomas (also called basal cell cancers). 
They usually develop on sun-exposed areas, especially the head and neck. Basal cell 
carcinoma was once found almost exclusively in middle-aged or older people. Now it is 
also being seen in younger people, probably because they are spending more time in the 
sun with their skin exposed.  
Basal cell carcinoma tends to be slow growing. It is very rare for a basal cell cancer to 
spread to nearby lymph nodes or to distant parts of the body. But if a basal cell cancer is 
left untreated, it can grow into nearby areas and invade the bone or other tissues beneath 
the skin.  
After treatment, basal cell carcinoma can recur (come back) in the same place on the 
skin. People who have had basal cell cancers are also more likely t