HPV causes cancer by producing two proteins that disable your cells’ built-in defenses against uncontrolled growth. These proteins, called E6 and E7, essentially switch off the molecular brakes that normally prevent damaged cells from multiplying. The process is slow: cancer typically takes years or even decades to develop after the initial infection, and about 90% of HPV infections are cleared by the immune system before any lasting damage occurs.
The Two Proteins That Drive It
When HPV infects a cell, its DNA instructs the cell to produce two key proteins. Each one attacks a different safety mechanism.
E6 destroys a protein called p53, often described as the “guardian of the genome.” Normally, p53 detects DNA damage in a cell and either pauses the cell cycle to allow repairs or triggers the cell to self-destruct if the damage is too severe. E6 tags p53 for disposal by the cell’s own recycling machinery, effectively removing the checkpoint that would catch dangerous mutations before they spread.
E7 disables a second brake called pRb. This protein normally keeps cells from entering the DNA-copying phase of growth until they receive the right signals. E7 forces pRb to release its grip, pushing cells into rapid, premature division. With both brakes disabled simultaneously, infected cells accumulate genetic errors and keep dividing anyway, exactly the conditions that lead to cancer.
Why the Virus Embeds Itself in Your DNA
In early infection, HPV exists as a separate loop of DNA floating inside the cell. But a critical turning point in cancer development is when that viral DNA physically inserts itself into the cell’s own chromosomes. This integration tends to break a viral gene called E2, which normally acts as a volume dial keeping E6 and E7 production in check. Once E2 is disrupted, production of both cancer-driving proteins ramps up with no off switch.
Integration does more than just boost E6 and E7. In a study of head and neck cancers, 82% of HPV integration sites overlapped with regions where the surrounding human DNA had been rearranged or amplified. The virus can land in the middle of genes that suppress tumors or repair DNA, breaking them. In one case, HPV inserted into a DNA repair gene and triggered a 28-fold amplification of the surrounding region, producing a nonfunctional version of the protein. In another, viral integration caused a 248-fold amplification of a nearby gene involved in cell growth. These disruptions create genomic instability, meaning the cell’s DNA becomes increasingly chaotic with each division.
How HPV Hides From Your Immune System
Most viruses trigger a rapid immune response, but HPV has evolved to stay under the radar. It infects only the outermost layer of skin or mucosal tissue, a region with limited immune surveillance, and it doesn’t kill the cells it infects. This means there’s no burst of debris to alert immune cells to a problem.
HPV also actively suppresses immune signaling within the infected cell. High-risk strains boost production of a cellular protein that blocks the relay of alarm signals from the cell’s pathogen sensors to its nucleus. This prevents the cell from producing interferons and the chemical messengers that would normally recruit immune cells to the area. Without that recruitment signal, the adaptive immune system never fully activates against the infection. This stealth is a major reason why some infections persist for years, giving E6 and E7 enough time to cause serious genetic damage.
Most Infections Never Become Cancer
The immune system clears about 90% of HPV infections within one to two years, with no lasting effects. Cancer only develops from the small fraction of infections that persist, and even then, the timeline is long. Persistent infection leads first to precancerous cell changes, which can sit at that stage for years before progressing further. Without that sustained pressure from E6 and E7 over a long period, the accumulation of genetic damage simply isn’t enough to produce a malignant tumor.
Several external factors influence whether a persistent infection progresses. Smoking roughly doubles to quintuples the risk among HPV-positive women, likely because tobacco chemicals cause additional DNA damage and reduce the number of immune cells in cervical tissue. Long-term oral contraceptive use (more than five years) has been associated with a fourfold increase in cervical cancer risk among HPV-positive women, possibly because hormonal changes promote viral DNA integration into the host genome. High numbers of full-term pregnancies also raise risk, in part because pregnancy hormones may weaken the local immune response to HPV and keep the most vulnerable area of the cervix exposed for longer periods.
Which HPV Types Are Dangerous
There are over 200 types of HPV, but only 12 are classified as high-risk: types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, and 59. Of these, HPV 16 and 18 are responsible for the majority of HPV-related cancers. The low-risk types, like HPV 6 and 11, can cause genital warts but do not lead to cancer.
HPV can cause six types of cancer: cervical, oropharyngeal (back of the throat, base of the tongue, and tonsils), anal, penile, vaginal, and vulvar. In the United States, oropharyngeal cancer has actually surpassed cervical cancer as the most common HPV-related malignancy. CDC data from 2018 to 2022 shows roughly 16,000 throat cancers per year attributed to HPV, compared to about 11,100 cervical cancers. This shift reflects both the success of cervical screening programs and a genuine rise in HPV-related throat cancers, particularly among men.
Screening and Vaccination
Current screening guidelines recommend that women aged 30 to 65 get a primary HPV DNA test every five years as the preferred approach. Co-testing with a Pap smear and HPV test every five years is also acceptable. For women aged 21 to 29, a Pap smear every three years remains the standard. Self-collected HPV testing is now recognized as an appropriate option for women 30 and older, removing a barrier for those who find clinical exams difficult to access.
Vaccination has already produced measurable results. Compared to 2008-2009, cervical precancer rates among screened women aged 18 to 20 dropped by 50% by 2014-2015. Among women aged 21 to 24, rates fell by 36%. The proportion of cervical lesions caused by HPV types targeted by the vaccine has dropped 40% in vaccinated women since the vaccines were introduced. Because the vaccine works by preventing infection rather than treating it, the full impact on cancer rates will continue to emerge over the coming decades as vaccinated generations age.