New research suggests babies who experience skull flattening as a result of their sleeping position most likely won't benefit from helmet therapy. 

A research team did not observe a difference in head shape between babies who had been treated with a sleeping helmet and those who had not, a BMJ-British Medical Journal news release reported.

About one in every five babies under the age of six months suffers from this type of skull deformation, called . A quarter of study subjects (one group that was treated with the helmet and another that received no treatment) in both groups made a full recovery.

Helmet treatment is controversial and expensive, but is fairly common in some countries.

The researchers looked at 84 healthy full-term babies who had moderate to severe skull deformities such as plagiocephaly, which causes one side of the head to become flattened.

Half of the babies in the study wore a tight-fitting helmet for 23 hours a day over the course of six months.

The team found 25.6 percent of babies who had helmet therapy achieved a full recovery by the age of two compared with 22.5 percent of those who did not.

The parents who used helmet therapy on their babies report side effects: 96 percent felt it imposed on their ability to cuddle with their child, 77 percent reported and unpleasant smell associated with the helmet, 71 percent reported excessive sweating, and 33 percent noticed their child was in pain, the news release reported.

The parents in both groups tended to be satisfied with their baby's head shape once they reached the age of two.

"Based on the effectiveness of helmet therapy, and the high prevalence of side-effects and high costs, we discourage the use of a helmet as a standard treatment for healthy infants with moderate to severe skull deformation," the researchers said, the news release reported.