Squamous cells are flat, thin cells that form the outer surface of your skin and line many of your organs. They’re one of the most common cell types in the human body, acting as a protective barrier between your internal tissues and the outside world. You’ve likely encountered the term on a lab result, a pathology report, or a screening test, and understanding what these cells do helps make sense of why they show up in so many medical contexts.
Shape, Structure, and What They Do
The word “squamous” comes from the Latin word for “scale,” and the name fits. These cells are large, flat, and tile-like, stacked in layers with a small nucleus at the center. They link together through tight junctions, essentially locking to their neighbors to form a continuous sheet. This arrangement creates a watertight barrier that can absorb everyday physical stress without breaking apart.
Squamous cells produce large amounts of a tough structural protein called keratin, which gives them their strength and a characteristic pinkish color under a microscope. Keratin is the same protein that makes up your fingernails, toenails, and hair. The primary job of squamous cells is protection: they shield deeper tissues from physical damage, prevent water loss through the skin, and block bacteria and other pathogens from entering the body.
Where Squamous Cells Are Found
Your body arranges squamous cells in two main ways depending on the job they need to do.
Stratified (multi-layered): In areas that face heavy wear, squamous cells stack roughly 20 rows deep. Your skin is the most obvious example. The outermost layers are fully flattened and packed with keratin, while deeper layers are rounder and still dividing to replace cells that slough off the surface. This multi-layered design also lines the mouth, throat, esophagus, and vagina.
Simple (single-layered): In places where substances need to pass through rather than be blocked, a single layer of squamous cells does the job. These ultra-thin membranes line your blood vessels, the tiny air sacs in your lungs, and body cavities like the chest and abdomen. Their thinness allows oxygen, carbon dioxide, and nutrients to diffuse across easily, supporting filtration, absorption, and secretion.
Keratinized vs. Non-Keratinized Cells
Not all squamous cells are equally tough. In areas exposed to friction and dry air, like the outer skin, the palate of your mouth, and your gums, the surface cells fill completely with keratin and die off, forming a hard, water-resistant shield. These are keratinized squamous cells.
In moist areas that need to stay flexible, like the inside of your cheeks, the floor of your mouth, the soft palate, and the lining of the esophagus, squamous cells remain alive at the surface and don’t fully harden. These non-keratinized cells still provide a barrier, but they’re softer and more permeable. The distinction matters medically because keratinized and non-keratinized tissues respond differently to infection and disease.
Squamous Cells on Lab Results
If you’re reading this because squamous cells appeared on a test result, context matters. Two of the most common scenarios are urinalysis and cervical screening.
Urine Tests
Squamous cells in a urine sample are typically reported as “few,” “moderate,” or “many.” A normal result is “few.” If your report shows moderate or many squamous cells, it usually means the sample was contaminated, picking up cells from the skin around the genital area rather than from the urinary tract itself. This often happens when the collection area isn’t cleaned thoroughly before providing the sample. Your provider may simply ask you to repeat the test with a cleaner catch.
Pap Smears
Cervical cancer screening specifically examines squamous cells from the cervix. Two results that cause the most confusion are ASC-US and ASC-H. ASC-US (atypical squamous cells of undetermined significance) is the most common abnormal Pap finding. It means some cells don’t look entirely normal, but the changes could be caused by irritation, a yeast infection, hormonal shifts during pregnancy or menopause, or benign growths rather than anything precancerous. ASC-H is a step further: some abnormal squamous cells were found that could represent a more significant change, and a closer examination called a colposcopy is typically the next step.
When Squamous Cells Become Cancerous
Because squamous cells cover so many surfaces, they’re a common starting point for cancer. Squamous cell carcinoma (SCC) can develop in the skin, lips, mouth, esophagus, lungs, cervix, vagina, and urinary tract. The underlying mechanism is the same across sites: DNA damage causes squamous cells to multiply uncontrollably instead of replacing themselves in an orderly way.
Skin squamous cell carcinoma is the most familiar type. Nearly 1.9 million cases were diagnosed worldwide in 2021, a 308% increase from 1990. Ultraviolet radiation from sunlight, tanning lamps, and tanning beds is the primary driver, directly damaging the DNA in skin squamous cells. HPV infection also raises risk, particularly for squamous cell cancers of the cervix, throat, and genital area.
Most skin squamous cell carcinomas are caught early and treated successfully with local removal. The outlook changes significantly when cancer spreads to lymph nodes or distant organs. In head and neck squamous cell carcinoma that has reached advanced lymph node involvement, for example, five-year survival drops to roughly 30%. This is why routine screening, whether through skin checks, Pap smears, or lung imaging for high-risk individuals, focuses so heavily on catching changes in squamous cells before they progress.
Reducing Your Risk of Squamous Cell Damage
Since UV exposure is the leading cause of squamous cell DNA damage in the skin, consistent sun protection is the most effective preventive step. That means sunscreen on exposed skin, protective clothing, and avoiding tanning beds entirely. For cervical squamous cells, HPV vaccination dramatically reduces the risk of the viral infections that trigger abnormal cell changes. Avoiding tobacco also matters: smoking is a major risk factor for squamous cell carcinoma in the lungs, mouth, and throat, as the chemicals in smoke directly damage the squamous lining of those organs.