Custom-made baby helmets do little to improve skull shape outcomes for infants, the New York Times reported.

Pediatricians have long recommended positioning newborns to sleep on their backs as a preventative measure against sudden infant death syndrome. However, one side effect of this sleeping technique is a flattened skull, which occurs in approximately one in five babies under the age of 6 months.

Helmets are a commonly recommended remedy that have been shown to normalize head shape, but a new study published in the British Medical Journal found the helmets offered minimal treatment effect.

Researchers in the Netherlands assigned 42 babies with misshapen skulls to wear a custom helmet for 23 hours a day for about six months. Another group of 42 babies with similar deformities was used as a control group. After two years, researchers measured the babies’ skull shape and found no significant differences between the two groups.

“I was very surprised at the results,” Dr. Mark R. Proctor, an associate professor of neurosurgery at Boston Children’s Hospital, told The New York Times, adding that the study was “rigorous.”

Helmet manufacturers question the study’s results, noting a helmet should not shift or rotate on an infant’s head, which was commonly reported by study parents.

“The value of this research is fully reliant upon the quality of the fit,” James Campbell, the vice president of the American Orthotic and Prosthetic Association, told The New York Times.

To avoid skull flattening without a helmet, some experts suggest repositioning a baby’s head while sleeping to shift pressure, having more tummy time, and limiting time spent in car seats in favor of a baby carrier. For babies with tight neck muscles, physical therapy may be a solution.

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