For decades, experts have estimated that 1 in every 5 Americans has experienced chronic pain at some point. Now, a recently released study from the National Institutes of Health (NIH) confirms such estimates. The question is, why? Why is chronic pain a bigger problem than even diabetes or depression?

The study in question analyzed data compiled from more than 10,400 adults who participated in multiple survey studies run by the CDC. Those previous studies asked participants to report how they felt in relation to pain over the previous three months. Some 21% reported chronic pain while 8% described high-impact chronic pain.

Chronic pain is generally defined as pain felt daily or almost daily for a minimum of three months. High-impact chronic pain is chronic pain severe enough to be life altering. The definitions notwithstanding, we are back to the question of why. Below are five possible explanations.

1. No Single Definition

At the top of the list is the fact that there is no single definition of chronic pain. The definition previously offered in this post is merely a general rule; it is not official, and it hasn’t been recognized by any medical organization as being the only definition. That being the case, patients do not have a concrete definition of chronic pain either. Without a hard and fast definition to rely on, how can we trust patient reports as accurate?

2. Pain Is a Relative Experience

Next up, the pain medicine doctors at Texas-based Lone Star Pain Medicine explain that pain is a relative experience. In other words, it is subjective. People experience pain in different ways, which is why pain clinics like Lone Star exist. The whole concept of pain medicine goes beyond what GPs and family doctors are able to do for patients whose experiences with pain don’t fit the norm.

Pain’s relative nature could encourage some people to report chronic pain even though it is not really an issue for them. Likewise, underreporting is also possible. There are people who tolerate pain very well, to the extent that they would not think of reporting a chronic situation even though they have experienced it.

3. Medical Marijuana’s Legality

As uncomfortable as it might be, we need to talk about the elephant in the room: medical marijuana’s legality across the country. More than three dozen states have approved medical marijuana as a treatment for chronic pain. It turns out that chronic pain is by far the most cited condition for people applying for medical marijuana cards. Could it be that incidences of chronic pain have increased, at least to some degree, because people are using it as an excuse to consume marijuana?

4. The Disability Option

On the same plane as medical marijuana’s legality is the disability option. Remember that chronic pain cannot be measured through a blood test, imaging test, etc. It can only be measured by patient reporting. Could it be that some incidences of chronic pain are simply a result of patients wanting to begin collecting disability payments? Anything is possible.

5. More Accurate Reporting

It could be that incidences of chronic pain only seem more rampant today because reporting methods were not so great in the past. Perhaps we are only seeing the results of better and more accurate reporting with modern numbers. Maybe 21% of the adult population has always suffered from chronic pain. We just don’t know.

The one thing we can say for sure is that chronic pain is a legitimate problem for millions of Americans. For that reason alone, we need to give it more attention.