Squamous means “scale-like.” The word comes from the Latin squama, meaning “the scale of a fish or serpent,” and it describes a specific type of cell in your body that is flat, thin, and layered like scales. You’ll most often encounter the term on a medical report, a lab result, or a diagnosis, where it refers to these flat cells or to conditions that affect them.
What Squamous Cells Look Like
Squamous cells are one of the basic building blocks of the tissue that lines your body’s surfaces, both inside and out. Under a microscope, they look like thin, flat sheets, almost tile-like, stacked together in overlapping layers. This is what distinguishes them from the other main cell shapes: cuboidal cells (which are roughly cube-shaped, with equal width, height, and depth) and columnar cells (which are tall and narrow, like columns).
The flat shape of squamous cells is not random. It’s what makes them good at two very different jobs depending on where they are in the body.
Where Squamous Cells Are Found
Squamous cells exist in two main arrangements. When they stack in multiple layers, they form what’s called stratified squamous epithelium. This is the tough, protective lining found in your skin, mouth, throat, esophagus, and vagina. The layering acts like armor: as the outermost cells get damaged or worn away, fresh cells underneath take their place. Your skin is the most obvious example.
When squamous cells sit in a single, paper-thin layer, they form simple squamous epithelium. This lining is found deep inside the lungs, in the tiny air sacs called alveoli. Here, the cells are so thin that oxygen and carbon dioxide can pass through them easily, moving between the air you breathe and your bloodstream. The same type of thin lining also coats the inside of blood vessels and the membranes surrounding your organs.
Why the Term Appears on Medical Reports
Most people first encounter the word “squamous” in one of two contexts: a Pap test result or a biopsy report. Understanding what it means in each case can take a lot of the anxiety out of reading those results.
Pap Test Results and ASCUS
One of the most common abnormal findings on a Pap test is something called “atypical squamous cells of undetermined significance,” often shortened to ASCUS. This means the lab saw squamous cells from your cervix that looked slightly unusual but not clearly abnormal. It is the most common abnormal Pap finding, and in many cases it turns out to be caused by something routine: an HPV infection, a yeast infection, inflammation, low hormone levels after menopause, or a benign growth like a cyst. An ASCUS result does not mean cancer. It typically means your doctor will want to do follow-up testing, often an HPV test, to determine whether anything needs closer monitoring.
Squamous Cell Carcinoma
When squamous cells become cancerous, the result is called squamous cell carcinoma, or SCC. Because squamous cells line so many surfaces in the body, this type of cancer can develop in several locations: the skin, lips, mouth, throat, esophagus, lungs, cervix, vagina, and urinary tract. Four sites account for the vast majority of cases: skin, head and neck, esophagus, and lungs.
Skin is the most common location by far. In the United States, age-standardized incidence rates for cutaneous squamous cell carcinoma have been measured at roughly 497 per 100,000 men and 296 per 100,000 women per year, making it one of the most frequently diagnosed cancers overall. Rates are even higher in Australia, where sun exposure is more intense. Most skin SCCs are caught early and are highly treatable.
In the lungs, squamous cell carcinoma is one of the subtypes of non-small cell lung cancer, which accounts for about 80 to 85 percent of all lung cancer cases. Lung SCCs tend to develop in the central airways of the lung, which distinguishes them from adenocarcinomas, another common lung cancer type that usually forms near the outer edges.
How Pathologists Identify Squamous Cells
When a biopsy is taken, a pathologist examines the tissue under a microscope to determine what kind of cells are present and whether they look normal. Squamous cells have several signature features. Normal squamous tissue shows flat cells connected by visible bridges between them, with a protein called keratin giving the cells structure. Keratin is the same protein that makes up your hair and nails, so it’s no surprise that skin cells produce a lot of it.
If squamous cell carcinoma is present, the pathologist looks at how closely the cancer cells still resemble normal squamous tissue. A “well-differentiated” tumor still has recognizable squamous features: the cells maintain their flat shape, produce keratin, and form distinctive round structures called keratin pearls. A “poorly differentiated” tumor has lost most of those features. The cells are disorganized, vary wildly in size and shape, divide rapidly, and produce little to no keratin. In general, well-differentiated tumors tend to be slower-growing and less aggressive than poorly differentiated ones.
If you see the word “squamous” on a pathology report, it is describing the cell type involved. It tells you which tissue the finding came from and helps your doctor determine the right next step, whether that’s routine monitoring or a more specific treatment plan.