HPV 16 and 18 spread primarily through skin-to-skin sexual contact. These two strains are classified as high-risk because together they cause about 70% of cervical cancers worldwide, but the way you contract them is the same as other HPV types: the virus enters through tiny breaks in the skin or mucous membranes during intimate contact with an infected person.
How the Virus Gets In
HPV doesn’t need a wound or visible cut to infect you. Microscopic tears in the skin’s surface, called microabrasions, are enough. These tiny disruptions in the outer layer of skin allow viral particles to reach the basal cells underneath, which is where the infection takes hold and begins replicating. This is why HPV spreads so efficiently: normal friction during sexual contact creates exactly the kind of microabrasions the virus needs.
The primary routes of transmission are vaginal sex, anal sex, and oral sex. But because HPV lives in skin cells rather than in blood or semen, any genital skin-to-skin contact can transmit it, even without penetration. Condoms reduce the risk but don’t eliminate it, since they don’t cover all the skin in the genital area.
Most People Never Know They Have It
HPV 16 and 18 rarely cause visible symptoms. Unlike low-risk HPV strains that produce genital warts, these high-risk types typically cause no outward signs at all. A global analysis of over 44,000 men across 35 countries found that about 31% had some form of HPV, with HPV 16 being the single most common strain at roughly 5% prevalence. Most of these men had no HPV-related health problems and wouldn’t have known they were infected without testing.
This silent nature is what makes HPV 16 and 18 so widespread. People transmit the virus without realizing they carry it, sometimes for months or years. There’s no routine HPV test for men, and cervical screening for women typically begins at age 21 or 25 depending on guidelines, meaning younger sexually active people can carry and spread the virus with no way of knowing.
What Happens After Infection
The good news is that most infections clear on their own. In a study tracking women aged 18 to 25, about 69% cleared HPV 16 within two years, and 85% cleared HPV 18 in that same window. By four years, clearance rates climbed to 82% for HPV 16 and 90% for HPV 18. Your immune system does the work here, gradually suppressing and eliminating the virus without treatment.
The concern is the minority of infections that persist. When HPV 16 or 18 lingers for years, it can cause cellular changes that progress toward cancer. HPV 16 carries the highest risk of any single strain. Current screening guidelines reflect this: if an HPV test comes back positive specifically for type 16 or 18, a closer examination of the cervix (colposcopy) is recommended even if a Pap smear looks normal. That’s because these two types are aggressive enough that waiting and retesting isn’t considered safe.
Factors That Raise Your Risk
Having more sexual partners increases your likelihood of encountering HPV simply through more exposure. But several other factors influence whether an infection takes hold and whether your body can clear it.
Your immune system plays the biggest role. People with weakened immunity, whether from conditions like HIV, medications that suppress the immune system, or other causes, are roughly 2.5 to 3.5 times more likely to have an active HPV infection. They’re also less likely to clear it, which raises the risk of long-term complications.
Smoking also matters. Smokers in one study had about three times the odds of testing positive for HPV compared to nonsmokers. Tobacco byproducts concentrate in cervical mucus and appear to weaken the local immune response, making it harder for your body to fight the virus in that specific tissue. Other factors linked to higher infection rates include having had multiple pregnancies and long-term use of oral contraceptives, though the biological reasons behind these associations are still being studied.
Non-Sexual Transmission
While sexual contact is overwhelmingly the main route, HPV 16 and 18 can spread in other ways. The most documented alternative is mother-to-child transmission during birth. A pooled analysis of nine studies covering over 2,100 women found that about 6.5% of babies born to HPV-positive mothers had detectable HPV. When mothers had active infections at delivery, transmission rates ranged from 5% to as high as 72% depending on the study. In one study of mother-baby pairs, 71% of the HPV types found in newborns matched their mother’s strain.
HPV DNA has also been detected in amniotic fluid before the membranes ruptured, suggesting the virus can sometimes reach the baby before delivery through ascending infection from the cervix. Most neonatal HPV infections clear on their own, but this route of transmission explains rare cases of HPV-related conditions in young children.
How Vaccination Protects Against These Strains
The HPV vaccine is the most effective way to prevent infection with types 16 and 18. The current nine-strain vaccine generates an immune response against both of these high-risk types (along with seven others). It works best when given before any exposure to the virus, which is why it’s recommended starting at age 9 to 12, well before most people become sexually active.
The vaccine teaches your immune system to recognize and block HPV before it can establish an infection. It produces antibody responses comparable to earlier vaccines that were proven to prevent HPV-related precancerous changes. For people who are already sexually active, the vaccine still offers protection against any strains they haven’t yet encountered.
How HPV 16 and 18 Are Detected
For women aged 30 to 65, current guidelines offer three screening options: a Pap test every three years, an HPV DNA test alone every five years, or both tests together every five years. The HPV DNA test can identify 14 high-risk strains individually, including types 16 and 18 specifically. This matters because a positive result for either of these two types triggers a more urgent response than a positive result for other high-risk strains.
If your screening comes back positive for HPV 16, which carries the highest cancer risk of any single type, colposcopy is recommended regardless of what your Pap results show. The same applies to HPV 18, which has a strong enough association with cancer that a normal Pap isn’t considered reassuring on its own. For other high-risk types, your doctor may take a watch-and-wait approach with repeat testing, but 16 and 18 get fast-tracked for closer evaluation.