HPV: Bare-Bones Basics

What Your Doctor May Not Tell You About HPV and Abnormal PAP Smears
By Joel Palefsky, M.D., Jody Handle

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First and foremost, I want you to understand that HPV only infects the skin, and the term in medicalese for skin is epithelium. The skin, or epithelium, lines not only our whole body, but also inside some of our internal organs.

Because of this particular trait, the only diseases caused by HPV are those of the skin. The skin is our coat of armor; it protects us from the environment and keeps us healthy. We have two kinds of skin: cutaneous and mucosal.

Cutaneous skin surfaces are what you usually think of as “skin”: the dry, occasionally hairy skin on your arms and legs. This kind of skin has a thick protective coating called keratin.

Mucosal skin surfaces, known as mucous membranes, are the wet ones: your mouth, vagina, and anus. These also contain keratin, but the protective coating is much thinner.

More than one hundred types of HPV infect humans. Like the skin, they're divided into two subgroups: those that infect cutaneous skin and those that infect mucosal skin. (HPVs are numbered 1, 2, 3, etc., much like hepatitis is lettered A, B, C, and so on.) Both types of HPV, cutaneous and mucosal, are spread through surface contact: from skin to skin, or mucous membrane to mucous membrane, or skin to mucous membrane, or mucous membrane to skin.... Imagine the possibilities! But since HPVs infect only the skin, they do not cause disease in other organs like the blood, bones, liver, heart (unless the skin cells infected with HPV spread to those organs in a process called metastasis, which I'll talk about later). Also, HPVs can't be acquired through a blood transfusion.

Cutaneous HPVs mostly cause warts on your skin-they're infectious and tenacious. (By the way, you don't get warts from toads! Lots of animals have their own papilloma viruses-rabbits, cows, dogs, to name a few. All papilloma viruses are extremely species specific and cannot be passed between species. So you can't get them by touching animals.)

HPV is particular in other ways. Not only does it only hang out in its own species (humans), but each of the more than one hundred HPV types has its own favorite hangout in the skin of the human body. Some HPV types prefer the cutaneous skin, and some prefer the mucosal skin. Some like the hands and feet, and some like the genital region. They rarely, if ever, cross over!

The most common skin HPV types are HPV 1, 2, and 4, and these cause warts on the hands (palmar warts) and feet (plantar warts). Almost all of us have had warts on the hands or feet at some time. Fortunately, HPV 1, 2, and 4 don't like to live in the skin of the genital tract, so these HPV types rarely-if ever-cause genital warts, precancerous genital lesions, or cancer. This means that you cannot get these lesions by touching the hands or feet of another person.

On the other hand, a group of HPV types do prefer the cutaneous and mucosal skin of the genital region. These HPV types can cause warts, precancerous lesions, or cancer in your genital area. As I mentioned earlier, the HPV types that are associated with cancer are called oncogenic. They're sometimes also called intermediate-risk or highrisk HPV types. The HPV types not associated with cancer-typically the ones that cause warts-are called nononcogenic, benign, or low-risk HPV types. The most common cancer-causing genital HPV types are HPV 16 and HPV 18, while the most common low-risk HPV types are HPV 6 and 11. While most of the thirty to forty known types of mucosal HPVs typically infect your genital tract, a few, such as HPV 13 and HPV 32, prefer the mucous membranes of the mouth.

Here's an important point about the skin-site preferences of the various HPV types. Since the genital HPV types live only in the genital skin, and since HPV is spread by skin-to-skin contact, then it seems as though most, if not all, genital HPV infection is sexually transmitted: It spreads by one person's genitalia touching another person's genitalia. Remember-the genital HPV types live only in the genital skin, and not in the other parts of your skin, such as your hands, face, and so on. So you can't get a genital HPV infection by touching the hand or foot of someone with warts in those places. To acquire a genital HPV infection, there usually needs to be genital-to-genital skin contact. Having said that, there are some other methods of sexual transmission, and I'll talk about them later.

Not all mucosal HPV types cause cancer, though. The chart above displays the cervical cancer risk of genital HPV types. Keep in mind, though, that “intermediate” risk doesn't mean those types won't cause cancer; it only means that they're found in fewer cancers. If you have an intermediate type, your risk of developing cancer may be similar to high-risk types.

Genital warts are caused by HPV types 6 and 11. These are the cauliflowerlike lesions, similar to other warts on your body, that can be found anywhere in the genital tract, including the anus, vulva, vagina, or penis. They're also nononcogenic-they won't cause cancer. But they're a pain, to be sure! I'll cover HPV 6 and 11 in great detail in part 4 of this book.

High or intermediate risk, or oncogenic, types don't always cause visible lesions, but they do cause cancer. In fact, 99 Percent of cervical cancers have been linked to oncogenic HPV types.

Copyright © 2002 by Dr. Joel Palefsky

About the Author

Dr. Palefsky is a professor at the University of California San Francisco and a leading HPV expert. Dr. Joel Palefsky and Jody Handley both live in San Francisco, CA.