Chester Higgins Jr. for The New York Times

Nobody likes going to the dentist, but redheads may have good reason.

A growing body of research shows that people with red hair need larger doses of anesthesia and often are resistant to local pain blockers like Novocaine. As a result, redheads tend to be particularly nervous about dental procedures and are twice as likely to avoid going to the dentist as people with other hair colors, according to new research published in The Journal of the American Dental Association.

Researchers believe redheads are more sensitive to pain because of a mutation in a gene that affects hair color. In people with brown, black and blond hair, the gene, for the melanocortin-1 receptor, produces melanin. But a mutation in the MC1R gene results in the production of a substance called pheomelanin that results in red hair and fair skin.

The MC1R gene belongs to a family of receptors that include pain receptors in the brain, and as a result, a mutation in the gene appears to influence the body’s sensitivity to pain. A 2004 study showed that redheads require, on average, about 20 percent more general anesthesia than people with dark hair or blond coloring. And in 2005, researchers found that redheads are more resistant to the effects of local anesthesia, such as the numbing drugs used by dentists.

The mutation in the MC1R gene also occurs in brunets, although it’s less common. In the latest study, the researchers tested for the MC1R gene variant, finding it in 65 of 67 redheads and in 20 of 77 people with brown or black hair. The participants were surveyed about dental-care anxiety, fear of dental pain and whether they avoid going to the dentist.

People with the MC1R gene variant had more dental care–related anxiety and fear of dental pain than those without the gene variant. And they were more than twice as likely to avoid dental care.

Dr. Daniel I. Sessler, an anesthesiologist and chairman of the department of outcomes research at the Cleveland Clinic, said he began studying hair color after hearing so many colleagues speculate about redheads requiring more anesthesia.

“The reason we studied redheads in the beginning, it was essentially an urban legend in the anesthesia community saying redheads were difficult to anesthetize,” Dr. Sessler said. “This was so intriguing we went ahead and studied it. Redheads really do require more anesthesia, and by a clinically important amount.”

After publishing research on the topic, Dr. Sessler began hearing from redheads who complained about problems with dental pain and fear about going to the dentist. He said that when someone with red hair is considering a dental or other procedure requiring an anesthetic, they should talk to their doctor about the high probability that they are resistant to anesthetics.

“Because they’re resistant, many redheads have had bad experiences,” Dr. Sessler said. “If they go to the dentist or have a cut sutured, they’ll need more local anesthetic than other people.”