You do everything you can to keep your tween safe and healthy, from getting her to bed on time to making sure he eats his veggies. But if you haven’t had your child vaccinated for human papillomavirus (HPV), it’s time to talk to your pediatrician. “HPV is the most common sexually transmitted infection,” says Mark Einstein, MD, chair of the department of obstetrics and gynecology at Rutgers NJ Medical School. “It’s spread by intimate skin-to-skin contact, [with or without] intercourse.”

Here’s what you should know about HPV and the vaccine:

About four out of five women contract HPV at some point in their lives. HPV is also common in men, and often has no symptoms, according to the CDC. Anyone who’s sexually active can get HPV, even if he or she’s only had sex with one partner. “A person with the virus has no symptoms, so it’s not like you can look and ‘see’ the infection and select an uninfected partner,” says Meg Fisher, MD, a former member of the American Academy of Pediatrics (AAP) Committee on Infectious Diseases and chair of the department of pediatrics at Monmouth Medical Center. “As teens experiment with touching or genital contact, that can spread the virus.”

HPV causes several kinds of cancer. There are many different types of HPV, and some of them cause cancer and genital warts. Most of the time, the body suppresses HPV and infections go away on their own without lasting health problems. However, in a small number of people, that’s not the case. “About 1 to 3 percent of people with HPV develop cancer, and there’s no way to predict who that’ll be,” says Einstein. Sadly, about 31,500 men and women get HPV-related cancers in the US each year.

The HPV vaccine works. “This vaccine prevents cancer in both boys and girls,” says Fisher. “Recent studies have shown we’re also seeing a decrease in the number of abnormal pap smears in girls who’ve been immunized.” The great news is that the vaccine prevents 90 percent of six types of HPV cancers: cervical, vaginal and vulvar cancers in women, penile cancer in men, and anal and throat cancers in both. And there’s another benefit: Although genital warts caused by HPV doesn’t lead to cancer, the vaccine also provides protection against them.

Age matters. It’s recommended your child get the shots stage 11 or 12, but they can start as early as age 9. Just like with measles or mumps, you want to vaccinate kids before they’re exposed. “You want your kids protected ahead of time, and we see the best immune response at these ages,” says Fisher. Your child can get the HPV shot at the same time as other recommended vaccines (Tdap, meningitis) for their age group.

They need a series of shots. Your child needs two HPV vaccine doses with 6 to 12 months between injections if he or she gets them by age 11 or 12; older kids need three doses. Cancer protection decreases as age at vaccination increases, so make sure the series is complete by age 13. Research indicates the protection lasts for at least 10 years, so no booster shot is currently recommended.

The vaccine has a good safety record. It’s been on the market since 2006, and more than 270 million doses have been distributed worldwide in more than 80 countries. No serious safety concerns have arisen. One note: Kids who have a severe allergy to yeast shouldn’t get the shot.

It’s a little uncomfortable. Like any injection, there can be mild side effects such as headache, fever or dizziness. And we’re not going to lie: It generally hurts. “It feels like a tetanus shot with heaviness and pain or redness at the injection site. We also have kids sit or lie down for 15 or 20 minutes afterwards because adolescents sometimes faint after a shot,” says Fisher.

The vaccine doesn’t promote risky sexual activity. An early concern was that it would encourage preteens and teens to engage in risky behaviors. “The data doesn’t show that. It actually encourages [a] discussion about sex,” says Einstein.

Arricca Elin SanSone is a New York-based health and lifestyle writer.