Four genes may help decide a person's pain threshold, research has shown.
Scientists studied the genes COMT, DRD2, DRD1, and OPRK1, in 2,721 people diagnosed with chronic pain.
Participants rated their perception of pain as "low", "moderate" or "high" on a scale from one to 10.
One gene, DRD1, was 33% more prevalent in the low pain group than in the high pain group, the researchers found.
DRD2 was 25% more common among those with high pain than those with moderate pain.
People in the "moderate" group were 25% more likely to have COMT and 19% more likely to have OPRK genes than those in the "high" group.
In total, 9% of participants had a low level of pain perception, while 46% had moderate pain and 45% high pain. All were taking opioid drugs for pain relief.
Study leader Dr Tobore Onojjighofia, from the US pain management company Proove Biosciences, said: "Our study is quite significant because it provides an objective way to understand pain and why different individuals have different pain tolerance levels.
"Identifying whether a person has these four genes could help doctors better understand a patient's perception of pain."
He added: "Chronic pain can affect every other part of life. Finding genes that may be play a role in pain perception could provide a target for developing new therapies."
The findings were presented at the annual meeting of the American Academy of Neurology in Philadelphia.