This electron micrograph shows a negatively stained human papilloma virus, or HPV, in human warts.

Cancers of the throat and back of the tongue linked to HPV and likely transmitted through oral sex are increasing, though still rare.

In August, the Centers for Disease Control released a report on the human papilloma virus, or HPV, today’s most common sexually transmitted disease, with good news and bad.

The good: Vaccination rates for HPV are increasing year by year, with a little more than 50 percent of young people fully vaccinated. The vaccine is recommended for all teens or children before their first sexual experience.

The bad: Rates of oropharyngeal cancers associated with HPV, transmitted through oral sex, continue to increase notably, especially among men, though it’s still an uncommon disease.

The CDC’s message strikes a tone of cautious alarm. The report called for more vaccination, which blocks the spread of the virus, and more research on oropharyngeal cancer. Most health experts agreed. Rates of HPV-associated oropharyngeal cancer have been rising slowly but steadily for years and are believed to be related to changing sexual behavior and more people enjoying oral sex. But less than 2 percent of the population gets the cancer.

“Everybody wants to know if they should be engaging in oral sex. What I tell them is the risk is not zero, but it’s very low,” said Brian R. Hill, the founder of The Oral Cancer Foundation, a national education and advocacy group, and a cancer survivor. “Is having oral sex more risky than driving your car on the freeway? There’s no question that driving your car is a lot more risky. I don’t think we should be afraid of oral sex.”

“I think it is important to keep the risk in perspective,” said Joel Palefsky, an infectious disease specialist at UCSF Medical Center.

“Even though the incidence of HPV-associated oral cancer is rising, particularly in men, it is still a relatively uncommon disease. For many people, the benefits of being able to enjoy the full range of sexual activity may outweigh the relatively small risk of oral cancer. But right now, there is optimism, with limited data, that the vaccines will protect against new exposures at all of the sites where HPV would ordinarily infect. Prevention measures boil down to a personal choice,” Palefsky said

There are around 200 strains of HPV, which live in the skin and many parts of the body. Some cause warts, including genital warts. Some prefer moist areas such as the genitals. The virus is common. Most people get HPV. If you’ve had sex, chances are you have, or have had, HPV. It’s also harmless for most. In about 80 percent of cases, HPV naturally clears within a few years, with no symptoms or effects. A few high-risk HPV strains are malicious and linked to cancers of the cervix, vulva, vagina, penis, anus, and throat and back of the tongue, known as oropharyngeal cancer.

The most prevalent HPV-associated cancers linked are oropharyngeal and cervical. The others are rare but also being closely watched. HPV-linked anal cancer is also increasing.

For the first time this year, HPV-associated oropharyngeal cancer rates surpassed those for cervical cancer. Recent CDC data shows that from 1999 to 2015, oropharyngeal rates increased 2.7 percent per year among men and 0.8 percent per year among women. At the same time, cervical cancer rates decreased 1.6 percent per year.Approximately 2,409 new cases of oropharyngeal cancer were diagnosed in females in 1999, and 6,966 in males. In 2015, this increased to 3,438 cases in females and 15,479 cases in males.

It’s still an uncommon cancer. According to the CDC, oropharyngeal cancer in general, regardless of HPV status, affects less than 2 percent of the population. Risk factors include being male, having more oral sex partners, smoking, and a compromised immune system. It’s believed women develop antibodies to the cancer sooner than men, fighting it more efficiently. While researchers aren’t sure what’s behind the increasing rates, many think it’s related to more engagement in oral sex, starting 25 years ago.

Because it takes decades for oropharyngeal cancer to develop, most don’t know they have it until it’s advanced. Treatment is promising, with a five-year survival rate of greater than 70 percent.

There isn’t a common FDA-approved test for HPV. It’s usually confirmed through laboratory tests when complications develop such as genital warts, an abnormal PAP smear, or cervical cancer.

Cervical cancer is the historical gateway to HPV knowledge. The virus is the primary cause of the cancer. When the HPV vaccine was introduced 12 years ago, it was given only to girls. The vaccine, combined with a routine Pap smear (screening for cervical cancer) are credited with significantly lowering cervical cancer rates. The vaccine prevents the spread of the virus; Pap smears detect early cancer, when it’s more successfully treated.

A public health success in the making, experts said. “This vaccine is the best way to protect our youth from developing cancers caused by HPV infection,” said CDC Director Robert R. Redfield, M.D., in the report. “Vaccination is the key to cervical cancer elimination.”

As more was discovered about HPV, boys were added to the recommendation in 2011. Today, it’s urged for all boys and girls before their first sexual experience.

It’s not proven if the HPV vaccine will also lower rates of oropharyngeal cancer. It takes decades for the cancer to develop, and the vaccine rates for boys are just ramping up. Effects won’t be seen for years. But scientific deduction makes a strong case.

“It’s been proven that the vaccine reduces oral HPV infection and separately proven that HPV infection causes oropharynx cancer,” said Gypsyamber D’Souza, an epidemiologist at Johns Hopkins University who studies HPV. “All of the scientific evidence that we have strongly supports the efficacy of the HPV vaccine to reduce oral HPV infection. We expect that the vaccine will reduce HPV related oral cancer.”

Public health experts aren’t suggesting people change their sexual practices to prevent oropharyngeal cancer. Condoms, dental dams (thin pieces of latex put over the vagina), monogamous relationships, and abstaining from oral sex could lower the spread of the virus, though HPV can spread around a condom.They are watching the data, advocating awareness, and stressing vaccines.

“With all STD’s there’s a balancing of risks and benefits. Individuals need to balance concern and what they do with their partners against the risk of this cancer which remains low, but is of course not zero,” D’Souza said.

She added: “We have a vaccine, and that is wonderful.”