Despite the widespread concern about HIV drug resistance, many people remain confused as to why it happens or what they can do to stop it.

Here is a primer that may help:

Drug resistance is caused when the environment of the viral pool is changed. When antiretroviral drugs are added to the mix, the viruses most able to survive take precedence over those that can’t. The survivors are what we refer to as resistant viruses.

Over time, the resistant viruses can become the dominant strain. This most often occurs when treatment is either stopped or interrupted, allowing the resistant variants to multiply and eventually predominate.

In most cases, wild-type HIV will predominate over all other variants. It is only when the viral pool is exposed to antiretroviral drugs that the make-up of the population will begin to change.

“Mutation” does not inherently mean “resistant.” The vast majority of these are so distorted they are unable to infect or even survive.

However, on occasion, a mutation will emerge that is able to infect host cells and survive in the presence of antiretroviral drugs. These mutations are drug-resistant.

While they are less “fit” than wild-type viruses, their ability to escape the effects of the HIV treatment give them a better chance of not only surviving but predominating.

Every now and then, a new resistant mutation will develop on top of the old one, increasing the fitness of the virus. As more and more of these mutations build, a virus can go from being a partially resistant virus to a fully resistant one.

When the drugs are no longer able to suppress the virus, treatment failure will be declared and a different combination of medications will be needed to restore suppression.

Having a resistant mutation doesn’t necessarily mean that your treatment will fail. This is because HIV therapy consists of three drugs, each of which can suppress multiple variants. So, if one of your drugs can’t suppress a certain variant, one or both of the remaining drugs usually can.

But, to do so means that you have to take your drugs every day. Having gaps in your treatment only allows resistant variants to replicate and start building additional, potentially harmful mutations.

According to research from the Centers for Disease Control and Prevention, around one of every six new infections in the U.S. involves a transmitted resistance to one or more antiretrovirals.

By doing so, your healthcare provider can select the combination of drugs best able to treat your unique viral population.

If you don’t take your drugs regularly, the levels in the bloodstream will begin to drop and allow the virus to replicate anew. While newer drugs are more “forgiving” and allow for the occasional missed dose, poor adherence still remains the primary cause of treatment failure.

In fact, according to research from John Hopkins University, fewer than 60 percent of Americans on antiretroviral therapy are able to achieve or sustain an undetectable viral load.

This was a common event with older HIV drugs like Sustiva (efavirenz) and Viramune (nevirapine), both of which belong to the same class of non-nucleoside drug. If you developed resistance, for example, to Viramune (which could happen easily with but a single mutation), you would most likely lose Sustiva as well.

While this is slightly less common with newer antiretroviral drugs, it is still not unusual to experience treatment failure and find that you’ve lost not only one or two drugs but an entire class of drug.

As a result, newly infected people may find themselves with fewer treatment options, while re-infected persons may be less able to achieve viral suppression even with complete adherence.

Optimal drug adherence and safer sex practices are key to not only reducing the risk of transmission but extending the lifetime of your HIV drugs.