Abnormal cells develop when DNA inside a cell becomes damaged or altered, and the cell’s built-in repair systems fail to fix the problem. This damage changes how cells grow, divide, and communicate, potentially leading to precancerous or cancerous conditions. The causes range from everyday biological processes happening inside your body right now to external exposures you can control.
How DNA Damage Creates Abnormal Cells
Every time one of your cells divides, roughly 3 billion DNA base pairs need to be copied. Even with high-accuracy copying machinery and a secondary error-correction system that catches mistakes with more than 99% efficiency, small errors still slip through at a rate of about one in every million to one hundred million bases per cell division. These uncorrected errors become permanent mutations the next time the cell divides, and they represent a constant, low-level source of new mutations throughout your life.
Beyond copying errors, DNA also sustains chemical damage just from normal metabolism. One common example: the DNA base cytosine spontaneously loses part of its chemical structure and transforms into uracil, which pairs with the wrong partner during replication. This creates a point mutation that alters the genetic instructions the cell follows. Similarly, oxygen-based chemical reactions inside cells damage guanine (another DNA base), causing it to mispair and add to the overall mutation count. These processes happen continuously in every cell.
Your cells have multiple repair systems designed to catch and fix these problems. When those repair pathways are themselves disrupted or overwhelmed, mutations accumulate faster than the cell can handle, destabilizing the genome and pushing cells toward abnormal growth.
Aging and Mutation Buildup
Scientists first proposed in the 1950s that mutations accumulating in non-reproductive cells might drive aging. Decades of research have since confirmed it. Studies now show a steady, clock-like buildup of mutations with age across nearly every tissue type, including liver cells, lung cells, brain neurons, and heart muscle cells. Tumors removed from older patients carry significantly more mutations than those from younger patients, reinforcing the connection between time and genetic damage.
As you age, the protective caps on the ends of your chromosomes (called telomeres) also shorten with each cell division. This shortening eventually disrupts gene activity in nearby regions of the chromosome, adding another layer of cellular instability on top of the mutations that have been quietly accumulating for decades. This is one reason cancer risk rises sharply with age, even in people with no obvious risk factors.
Lifestyle Factors: Tobacco and Alcohol
Tobacco smoke and alcohol are among the most well-documented causes of cellular damage. Smoking introduces dozens of compounds that directly bind to DNA and create what are called “adducts,” physical distortions in the DNA strand that interfere with normal copying and gene activity. The cancer risk from smoking has grown over time as smoking patterns have changed. In contemporary data, women who smoke face roughly 26 times the risk of dying from lung cancer compared to women who have never smoked. For men, the figure is about 25 times the risk.
Alcohol metabolism also generates reactive compounds that damage DNA. Combined with genetic susceptibility, hormonal factors, and other exposures, these lifestyle-driven insults create sequence changes at the cellular level that disrupt normal growth regulation.
Environmental Carcinogens
Certain chemicals in the environment cause specific, well-characterized types of DNA damage. The variety is broader than most people realize:
- Polycyclic aromatic hydrocarbons (from vehicle exhaust, grilled food, and industrial pollution) create bulky chemical attachments on DNA bases, physically warping the DNA strand and blocking normal replication.
- Nitrosamines (found in processed meats and tobacco products) add small chemical groups to DNA bases, particularly guanine, altering how they pair during cell division.
- Mycotoxins (produced by mold on grains and nuts) target guanine bases and cause a specific type of mutation in the TP53 gene, one of the most important tumor-suppressing genes in the body.
- Asbestos causes damage through a different route: it generates oxidative stress that breaks DNA strands, triggers chronic tissue scarring, and physically interferes with the machinery cells use to divide.
- Heterocyclic aromatic amines (formed when meat is cooked at high temperatures) cause strand breaks and chromosomal damage, particularly in guanine-rich regions of the genome.
Ultraviolet Radiation and Skin Cells
UV radiation from the sun is the most common environmental carcinogen. It works through a very specific mechanism: UV energy causes neighboring DNA bases (specifically pyrimidines) to fuse together, forming structures called pyrimidine dimers. These fused bases distort the DNA strand and block both copying and gene reading. If the cell’s repair systems don’t remove the dimers before the next round of division, the damage becomes a permanent mutation. This is the direct chemical link between sun exposure and skin cancer.
Chronic Inflammation
Short-term inflammation is a normal healing response. Chronic inflammation, the kind that persists for months or years, is a different story. It creates an environment where cells are bathed in growth-promoting signals and reactive oxygen species that damage DNA. The effect is like a wound that never finishes healing: the body keeps sending signals to grow and repair tissue, and those same signals accelerate the emergence of abnormal cells from precancerous lesions.
Over time, chronic inflammation promotes both direct mutations and changes in how genes are switched on and off (called epigenetic alterations). These changes can disable tumor suppressor genes and activate growth-promoting genes, pushing cells further down the path toward uncontrolled division. Conditions that involve long-term inflammation, such as inflammatory bowel disease, chronic hepatitis, and certain autoimmune disorders, are associated with higher cancer risk for this reason.
Viral Infections
Certain viruses directly reprogram cells in ways that lead to abnormal growth. Human papillomavirus (HPV) is the most studied example. High-risk strains of HPV infect cells in the cervix and other tissues and interfere with the molecular controls that regulate cell division and communication. Infected cells begin multiplying in an uncontrolled way, and over time, this can progress from mild cellular changes to precancerous dysplasia to invasive cancer. The same basic mechanism applies to HPV-related cancers in the throat, anus, and other sites.
Inherited Genetic Changes
Up to 10% of all cancers may be caused by inherited genetic changes. You can’t inherit cancer itself, but you can inherit a mutation that dramatically raises your risk. The most well-known examples are mutations in the BRCA1 and BRCA2 genes. A child who inherits a mutated copy of either gene from a parent has a much higher lifetime risk of developing breast cancer, ovarian cancer, and several other types.
These inherited mutations typically affect genes responsible for repairing DNA damage or suppressing tumor growth. With one copy of the gene already non-functional from birth, it takes only one additional hit to the remaining working copy for the cell to lose that protective function entirely. This is why inherited cancer syndromes tend to cause cancer at younger ages than is typical.
What “Abnormal Cells” Actually Means on a Report
If you’ve been told you have abnormal cells, it helps to understand the terminology. Not all abnormal cells are the same, and the distinctions matter for what happens next.
In hyperplasia, there are more cells than normal, but each individual cell looks normal under a microscope. In dysplasia, the cells themselves look abnormal, but they are not cancer. Dysplasia is graded as mild, moderate, or severe depending on how visually distorted the cells appear and how much of the tissue is affected. Severe dysplasia sits closest to cancer on the spectrum but is still considered precancerous, meaning it has not yet gained the ability to invade surrounding tissues.
Many cases of mild dysplasia resolve on their own as the body’s immune system and repair mechanisms clear the damage. Moderate and severe dysplasia are more likely to need monitoring or treatment, but a diagnosis of abnormal cells is not a cancer diagnosis. It is a signal that something has shifted at the cellular level and warrants attention.