Human papillomavirus, or HPV, is an incredibly  common sexually transmitted infection that  
Human papillomavirus, or HPV, is an incredibly  common sexually transmitted infection that  

affects humans of all genders worldwide. In the  United States alone, CDC estimates that upwards  
affects humans of all genders worldwide. In the  United States alone, CDC estimates that upwards  

of 79 million Americans currently have HPV, and  that around 14 million people will become newly  
of 79 million Americans currently have HPV, and  that around 14 million people will become newly  

infected each year. Truly, HPV is so common that  essentially every person who is sexually active  
infected each year. Truly, HPV is so common that  essentially every person who is sexually active  

will likely get HPV at some point in their  life, provided they don’t get the HPV vaccine. 
will likely get HPV at some point in their  life, provided they don’t get the HPV vaccine. 

It turns out papillomaviruses aren’t unique to  humans, they’re actually exceptionally common  
It turns out papillomaviruses aren’t unique to  humans, they’re actually exceptionally common  

throughout the animal kingdom. But each  virus can only infect a single species.  
throughout the animal kingdom. But each  virus can only infect a single species.  

Depending on the host, papillomaviruses  are capable of causing lytic, chronic,  
Depending on the host, papillomaviruses  are capable of causing lytic, chronic,  

latent, and transforming infections. Human  papillomaviruses in particular can cause warts,  
latent, and transforming infections. Human  papillomaviruses in particular can cause warts,  

and several genotypes of these viruses are  associated with certain types of cancer. 
and several genotypes of these viruses are  associated with certain types of cancer. 

Papillomaviruses are part of the Papillomaviridae  family, and they are small, non-enveloped viruses  
Papillomaviruses are part of the Papillomaviridae  family, and they are small, non-enveloped viruses  

with icosahedral capsids and double-stranded DNA  genomes. The tricky thing about papillomaviruses  
with icosahedral capsids and double-stranded DNA  genomes. The tricky thing about papillomaviruses  

is that they encode proteins that promote cell  growth. From a virus’ standpoint, that’s great.  
is that they encode proteins that promote cell  growth. From a virus’ standpoint, that’s great.  

The ability to promote cell growth helps the  virus carry out a lytic replication cycle.  
The ability to promote cell growth helps the  virus carry out a lytic replication cycle.  

From a human or animal’s perspective, it’s  not the best news for a few reasons. First,  
From a human or animal’s perspective, it’s  not the best news for a few reasons. First,  

as we recall, lytic replication essentially  means the virus infiltrates a host cell,  
as we recall, lytic replication essentially  means the virus infiltrates a host cell,  

uses all the host cell machinery to replicate  many times, and then explodes its way out of the  
uses all the host cell machinery to replicate  many times, and then explodes its way out of the  

host cell, destroying it and delivering  new virions to the surrounding cells.  
host cell, destroying it and delivering  new virions to the surrounding cells.  

Second, these viruses have the potential to  oncogenically transform a nonpermissive cell,  
Second, these viruses have the potential to  oncogenically transform a nonpermissive cell,  

which basically means triggering uncontrolled cell  growth. This is known by another name, cancer. 
which basically means triggering uncontrolled cell  growth. This is known by another name, cancer. 

Over 100 types of human papillomaviruses  have been identified, which are classified  
Over 100 types of human papillomaviruses  have been identified, which are classified  

based on their DNA sequence homology. HPV  can be further subcategorized depending  
based on their DNA sequence homology. HPV  can be further subcategorized depending  

on the type of tissue they infect, as either  cutaneous HPV, which means infecting the skin,  
on the type of tissue they infect, as either  cutaneous HPV, which means infecting the skin,  

or mucosal HPV, which means infecting mucosal  membranes. Within the mucosal HPV category,  
or mucosal HPV, which means infecting mucosal  membranes. Within the mucosal HPV category,  

there is a group of viruses associated with  cervical cancer. But more on that in a moment. 
there is a group of viruses associated with  cervical cancer. But more on that in a moment. 

Human papillomavirus is transmitted  sexually through skin-to-skin contact.  
Human papillomavirus is transmitted  sexually through skin-to-skin contact.  

Let’s break down what happens next. The virus is  able to enter the basal layer of the epidermis  
Let’s break down what happens next. The virus is  able to enter the basal layer of the epidermis  

through tiny breaks in the skin. Once  inside, the virus triggers cell growth,  
through tiny breaks in the skin. Once  inside, the virus triggers cell growth,  

which allows the virus to make even more copies of  itself, since more host cells means more virions.  
which allows the virus to make even more copies of  itself, since more host cells means more virions.  

All those extra cells are what cause warts, a  potential symptom of HPV. Of course, not everyone  
All those extra cells are what cause warts, a  potential symptom of HPV. Of course, not everyone  

infected with HPV develops warts, and in fact,  most people who get HPV have no symptoms at all. 
infected with HPV develops warts, and in fact,  most people who get HPV have no symptoms at all. 

So, why does it vary so much?  HPV expresses different viral  
So, why does it vary so much?  HPV expresses different viral  

genes depending on the type and layer  of skin that the virus has broken into,  
genes depending on the type and layer  of skin that the virus has broken into,  

with the added variable that the different types  of HPV are very tissue-specific. In particular,  
with the added variable that the different types  of HPV are very tissue-specific. In particular,  

two strains of the virus, HPV-16 and HPV-18,  are responsible for about 70% of cervical  
two strains of the virus, HPV-16 and HPV-18,  are responsible for about 70% of cervical  

cancer cases. The other 30% of cancer cases are  caused by a dozen or so “high risk” HPV strains. 
cancer cases. The other 30% of cancer cases are  caused by a dozen or so “high risk” HPV strains. 

Yet another thing that helps this virus spread so  easily is the fact that a person infected with HPV  
Yet another thing that helps this virus spread so  easily is the fact that a person infected with HPV  

can still pass the virus to someone even if  they have no visible symptoms. In most cases,  
can still pass the virus to someone even if  they have no visible symptoms. In most cases,  

HPV goes away on its own without causing any  health problems. But for those cases where HPV  
HPV goes away on its own without causing any  health problems. But for those cases where HPV  

sticks around, it can cause either genital warts,  which can be treated with prescription medication,  
sticks around, it can cause either genital warts,  which can be treated with prescription medication,  

or different kinds of cancer. In addition to  cervical cancer and other genital-specific  
or different kinds of cancer. In addition to  cervical cancer and other genital-specific  

cancers, HPV can also cause cancer in the back of  the throat. Cancers caused by HPV can take years  
cancers, HPV can also cause cancer in the back of  the throat. Cancers caused by HPV can take years  

or even decades to develop, so it’s always  a good idea to get regular check-ups.  
or even decades to develop, so it’s always  a good idea to get regular check-ups.  

For women between the ages of 21 and 65, getting  regular screenings can catch the very early stages  
For women between the ages of 21 and 65, getting  regular screenings can catch the very early stages  

of cancer and prevent it from developing. Ultimately, there are a number of ways  
of cancer and prevent it from developing. Ultimately, there are a number of ways  

that you can lower your chances of getting HPV. Of  course, proper condom use can help. There’s also  
that you can lower your chances of getting HPV. Of  course, proper condom use can help. There’s also  

an HPV vaccine that’s safe and effective against  cancer-causing strains of HPV. Either way, making  
an HPV vaccine that’s safe and effective against  cancer-causing strains of HPV. Either way, making  

sure to visit the doctor for regular check-ups can  catch issues before they become more serious, just  
sure to visit the doctor for regular check-ups can  catch issues before they become more serious, just  

the same as pretty much all health conditions.  And that covers the basics regarding HPV.
the same as pretty much all health conditions.  And that covers the basics regarding HPV.