Squamous Metaplasia: Understanding Cellular Changes
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer: What is squamous metaplasia?
Squamous metaplasia is a condition in which the cells lining an organ, gland or passageway change into flat, scale-like squamous cells. Most forms are benign and do not raise cancer risk, but the keratinizing type may be precancerous if not monitored. Triggers include chronic irritation, HPV, smoking and vitamin A deficiency, and regular screening tracks progression.
When to see a doctor
Squamous metaplasia often causes no symptoms. [1] See a healthcare provider if you have an urgent need to urinate that doesn't go away, repeated urinary infections, a persistent white patch in your mouth, or an abnormal screening result, and keep up with recommended cervical screening. Blood in the urine or any persistent, unexplained symptom should be checked promptly.
What the research says
Keratinizing metaplasia of the bladder needs follow-up, even if it isn't strictly precancerous. A literature review found that keratinizing squamous metaplasia of the bladder is rare and that the risk of malignant transformation rises with dysplasia and with extensive keratinization. The authors concluded there is not enough data to call it a premalignant condition unless dysplasia is present, but that all patients should have regular follow-up (Ahmad et al., Urologia Internationalis, 2008) [2].
Both types can carry early cancer-related gene changes. In biopsies from the urinary tract, TERT promoter mutations were found in 94% (15) of invasive cancer foci, but also in 68% (13) of keratinizing and 70% (7) of nonkeratinizing metaplasia foci, including in people with chronic bladder dysfunction and no cancer. [3] The findings suggest a possible molecular route from chronic irritation to cancer, although the study was small (Taylor et al., European Urology Open Science, 2022).
Smoking is linked to squamous metaplasia in the breast ducts. In 29 patients with squamous metaplasia of the lactiferous ducts (Zuska's disease) seen at one center, 11 (37.9%) were current or former smokers, and the authors confirm a strong association with smoking (Abdelwahab et al., Dermatology, 2024) [4].
What Is Squamous Metaplasia?
Squamous metaplasia happens in the epithelium, the thin layer of tissue that lines and protects many parts of the body. In metaplasia, one mature cell type is replaced by another mature cell type that isn't normally found in that tissue. It is essentially a survival mechanism: cells adapt to stress or a changed environment by becoming a tougher cell type. Although the term sounds alarming, these changes are often part of the body's normal response to irritation or hormonal shifts.
What are the types of squamous metaplasia?
Healthcare professionals classify squamous metaplasia by whether the cells produce large amounts of the protein keratin. [1] This distinction matters for the outlook and for whether follow-up is needed.
Type | Description | Cancer risk |
|---|---|---|
Nonkeratinizing | Cells transform without accumulating excess protein | Noncancerous and generally harmless; no increased risk |
Keratinizing (can look like leukoplakia in the mouth) | Cells produce excess keratin, forming a protective but abnormal layer | May be precancerous; requires monitoring |
If keratinizing metaplasia is left untreated, it can first progress to dysplasia [1] (abnormal, irregular cells), which is more likely to become cancer. For the mouth version, see our guide to leukoplakia, and for another example of precancerous HPV-related cell changes, see our article on anal dysplasia.
Where does squamous metaplasia occur, and what triggers it?
Squamous metaplasia can develop wherever epithelial tissue exists [1], but it is most often found in a few organ systems. The triggers depend on the location. [1]
Affected area | Potential triggers and risk factors |
|---|---|
Cervix | Human papillomavirus (HPV), hormonal changes during childbearing years or menopause |
Bladder | Frequent urinary tract infections (UTIs), kidney stones, or long-term catheter use |
Respiratory tract | Smoking, chronic obstructive pulmonary disease (COPD), or vitamin A deficiency |
Urinary system | A history of radiation or hormone therapy for certain cancers |
Learn more about some of these triggers in our guides to urinary tract infections, kidney stones, and oral HPV.
Cervical squamous metaplasia
In the cervix, nonkeratinizing squamous metaplasia is very common and is considered a normal difference rather than a disease. HPV infection can cause cell changes, but not everyone with the virus develops precancerous changes. [1]
What are the symptoms of squamous metaplasia, and how is it detected?
In many cases squamous metaplasia causes no symptoms and is found only during routine screening. When symptoms occur, they relate to the underlying irritation or the organ involved. For example, bladder involvement can cause urge incontinence (a sudden, urgent need to urinate) [1], while cervical changes may cause mild inflammation or discomfort.
Diagnosis depends on the area. Cervical changes are often caught during Pap smears or HPV tests. In other areas, a biopsy may be performed, in which a small tissue sample is examined under a microscope by a specialist to confirm the type of cell change. [1]
How is squamous metaplasia managed, and what is the outlook?
Management depends on the type of cell change. Nonkeratinizing forms, particularly in the cervix, are considered normal variations and rarely need treatment. [1] If keratinizing metaplasia is found, regular follow-up appointments are needed to make sure the cells do not progress to dysplasia or cancer. [1] Your provider will also look for the cause, such as an infection, irritation, or smoking, because addressing it may allow cells to return to normal. If you smoke, see our guide to nicotine replacement therapy for help quitting.
Conclusion
Squamous metaplasia is a common and often manageable cellular adaptation. Knowing the difference between the benign nonkeratinizing type and the keratinizing type that may be precancerous is the first step in managing it. Keeping up with screenings and addressing risk factors such as smoking and chronic infection helps prevent complications.
What are the next steps for squamous metaplasia?
If you've received a diagnosis involving cell changes, ask your healthcare professional what type you have and what monitoring schedule is right for you.
Trusted resources: Cleveland Clinic: Squamous Metaplasia
Frequently Asked Questions
Is squamous metaplasia a form of cancer?
No. It is a noncancerous change in cells, although the keratinizing type may become precancerous if it is not monitored.
What does "metaplasia" mean?
The term "metaplasia" means one mature cell type is replaced by another mature cell type that isn't normally found in that tissue.
Can smoking cause these cell changes?
Yes. Smoking is a major risk factor for squamous metaplasia in the airways and has also been linked to it in other tissues.
Is cervical squamous metaplasia common?
Yes. Nonkeratinizing cervical squamous metaplasia is very common in women and is considered a normal difference.
Does HPV always lead to metaplasia?
No. HPV can cause cell changes, but not everyone with the virus develops precancerous changes.
What is keratin?
Keratin is a protein that helps form skin, hair, and nails. In keratinizing metaplasia, excess keratin builds up and forms an abnormal layer.
Are there symptoms of bladder metaplasia?
Some people have urge incontinence, which is a sudden, urgent need to urinate. Many have no symptoms.
How is it diagnosed?
Usually through a Pap smear or HPV test (for the cervix) or through a tissue biopsy examined under a microscope.
Does vitamin A deficiency play a role?
Yes. A lack of vitamin A can lead to squamous metaplasia in the airways and respiratory system.
What is the difference between metaplasia and dysplasia?
Metaplasia is a change from one normal cell type to another. Dysplasia involves abnormal, irregular cells that are more likely to become cancerous.
Can radiation therapy cause these changes?
Radiation therapy for certain conditions can trigger metaplasia in the urinary tract.
Is treatment always necessary?
No. Nonkeratinizing types rarely need treatment, but keratinizing types require regular monitoring.
Does cervical squamous metaplasia need treatment?
Usually not. The nonkeratinizing type is a normal variation, and your provider will advise you on screening based on your test results.
Can metaplasia be reversed?
In some cases, addressing the underlying cause, such as stopping smoking or treating an infection, may allow cells to return to normal.
What happens if it goes untreated?
Keratinizing types can progress to dysplasia and, in some cases, to squamous cell carcinoma if they are not monitored and managed.
Related Reading
Intestinal Metaplasia: Understanding Cellular Changes in the Stomach explains how stomach lining cells change and when monitoring is needed.
What Is Cervical Dysplasia (Cervical Intraepithelial Neoplasia)? explains precancerous cervical cell changes, their grades and treatment options.
Leukoplakia Symptoms, Causes, and Treatment: What White Mouth Patches Mean explains what white mouth patches mean and when they need a biopsy.
Pap Smear (Pap Test): Age, Procedure, Results and How Often to Get One explains how the Pap test screens for abnormal cervical cells.
References
Cleveland Clinic. Squamous Metaplasia. Cleveland Clinic. June 15, 2022. https://my.clevelandclinic.org/health/diseases/23307-squamous-metaplasia
Ahmad I, Barnetson RJ, Krishna NS. Keratinizing squamous metaplasia of the bladder: a review. Urologia Internationalis. 2008;81(3):247-251. PMID 18931537. https://doi.org/10.1159/000151398
Taylor AS, Newell B, Chinnaiyan AM, et al. TERT promoter mutations in keratinizing and nonkeratinizing squamous metaplasia of the urinary tract. European Urology Open Science. 2022;35:74-78. PMID 35024637. https://doi.org/10.1016/j.euros.2021.11.007
Abdelwahab RM, Aghazadeh Mohandesi N, Sturgis CD, et al. Squamous metaplasia of lactiferous ducts (Zuska's disease) of the breast: clinical and histopathologic manifestations. Dermatology. 2024;241(2):210-215. PMID 39541956. https://doi.org/10.1159/000542622
Medical Disclaimer
This article is for informational purposes only and does not constitute medical advice. Always seek the advice of a qualified healthcare professional with any questions you may have regarding a medical condition.
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