You might know of it as a sexually transmitted infection that causes uncomfortable warts,

the papilloma, but you also may have heard that it can lead to a deadly form of cancer.

Both are actually true, as is the possibility that you can have HPV and experience no symptoms whatsoever.

HPV isn't just one virus.

There are actually over 200 strains, and the different types of HPV can result in different

outcomes (which we'll get into a little bit later).

But first, before HPV can do anything, it has to find a way into your skin.

Hi, I'm Dr. Moscicki from the University of California Los Angeles, Department of Pediatrics.

I'm chief of adolescent and young adult medicine, and I have been studying HPV for over 30 years now.

So when you're looking at skin, you have several layers, and you have the very basal cell layer,

that is, the layer that sits right on top of the basement membrane, and right under

that is what we call the dermis.

and on top of that, you have the spinous, and eventually, you get the very top cornified cell layers.

HPV first attaches itself to the basement membrane, by entering the body through a wound or micro-abrasion.

It usually does this through sexual intercourse, but there are other types of HPV that cause

hand and foot warts that aren't sexually transmitted.

Reaching the basement layer is key because there is a receptor there that it must attach to first.

It's referred to as a heparan sulfate receptor.

This receptor actually changes the virus so that it can then attach to the basal cells.

Once it does this, it injects its DNA into the cell's nucleus.

As the basal cells matures, the infected cell makes its way to the very top.

...it kind of hijacks the cell.

And what it does is it makes it start proliferating a lot so that it can replicate itself.

This all happens without your body mounting a real defense against the disease, because

HPV avoids expressing genes that would initiate an immune response until later in its lifecycle.

it looks like it's a mechanism that HPV has developed in order for its own survival.

But, while HPV has found a clever way to avoid the immune system, the body can still get rid of the infection.

Like, you know, when you're taking a shower, that top layer of skin kind of comes off.

...once it gets sloughed off, if there's no other place to invade, then that infection's

just gonna burn out very quickly.

That it was a one-time chance that it found access to the basement membrane.

In fact, even though 80% of people in the United States are thought to contract HPV,

90% of infections are cleared on their own.

So, if the infection doesn't usually last, whats t'he big deal?

Well, that's where those different types of HPV become really important, specifically

the ones that can cause cancer.

There's only about 13 types that we have associated with cancer, and they all fall into the alpha types.

The most famous ones are type 16 and 18.

They're actually responsible for around 70% of cervical cancers.

Types 16 and 18  are totally different from the types of HPV that cause warts, which aren't

pleasant but fortunately do not typically become cancerous.

What we believe, the way it causes cancer, is that it infects, probably, a stem cell within the basal cell layer.

Therefore, those stem cells, as it maturates, what happens is, literally, HPV hijacks the

host cell machinery, says, I want you to replicate, because every time you don't stop me, I can

make more and more of my DNA.

While replicating in stem cells, these oncovirus types of HPV will express the genes called E6 and E7.

These oncoproteins stop the body from killing and clearing out cells with damaged DNA, allowing

the cancerous cells to continue replicating.

So when there's a damaged cell, it's a race.

Their immune system is probably trying its best, but it's really pushing the system,

that it's replicating way faster than the immune system can even access it.

Fortunately, we have ways to prevent HPV from getting to this point.

First, there are screenings for cervical cancer that can catch the disease when it is still pre-cancerous.

But there is an unfortunate lack of screening methods for the other cancers caused by HPV.

For people who are young enough and have not been exposed to HPV, there is also a very

effective vaccine has been available since 2006.

And while some people might think it's only given to girls because of the risk of cervical cancer,

It's recommended for boys as well.

So the prevention here, we're talking about anal cancer, penile cancers, and oropharyngeal cancers.

So it's equally as important for boys to get this vaccine as it is for girls.