FRIDAY, May 2, 2014 (HealthDay News) -- Some babies develop a flat area on their head from lying in the same position for long periods of time, but special helmets are ineffective in treating the condition, a new study finds.

How effective are helmets for plagiocephaly?

Among infants with mild-to-moderate plagiocephaly, helmet therapy was rated successful in 83 percent of those who started before 24 weeks. The success rate decreased to 69 percent for infants starting treatment between 24 and 32 weeks and 40 percent when treatment was started at 32 weeks or later.

Is a helmet necessary for flat head?

Helmet therapy for plagiocephaly is always a choice; it's never mandatory. It can be helpful in the right situation, but it's not always needed. The head shape does often get better, with or without the use of a helmet.