People with red hair seem particularly nervous about visiting the dentist, and genetics may explain why, according to a new study.

A few studies in recent years have found that redheads tend to be less responsive to local pain-blockers like Novocain and may need larger doses to get the same pain relief as people with darker coloring.

These latest findings, published in the Journal of the American Dental Association, suggest that the genetics of red hair may be behind the link.

Red hair is the result of particular variations in what is called the melanocortin-1 receptor (MC1R) gene, which helps determine pigmentation. While it was once thought that the gene was active only in the skin, hair and eyes, more-recent research has shown that it also functions in the brain, where it may play a role in processing pain, anxiety and fear.

So for the new study, researchers led by Dr. Catherine J. Binkley, of the University of Louisville in Kentucky, looked at whether red hair and MC1R variations were related to people's aversion to seeing the dentist.

They found that among the 144 white adults they recruited, those with MC1R variations reported more anxiety about dental procedures and were twice as likely to say they avoided the dentist altogether.

Not surprisingly, nearly all of the natural redheads in the study carried at least one copy of an MC1R variation linked to red hair — 65 of 67 participants. The same was true of roughly one-quarter of the 77 dark-haired study participants.

When the researchers took a closer look at the data, they found that the presence of these MC1R variations was more strongly linked to dental anxiety than was hair color itself.

The results, according to Binkley's team, suggest that dentists should ask all patients — but especially redheads — about their anxiety over any procedures they must have and then use "appropriate modalities" to help them manage the problem.

SOURCE: Journal of the American Dental Association, July 2009.