There's a strange explanation behind why a number of babies in North Carolina, US, were testing positive for marijuana.

A new study suggests that certain baby soaps may be behind the surprising finds, MSNBC reports.

The researchers began their investigation after nurses at a North Carolina hospital were concerned as the number newborns testing positive for marijuana steadily rose.

In the study, urine samples that had traces of five baby soaps tested positive for tetrahydrocannabinol (THC), the active ingredient in marijuana.

Only a minute amount of the soaps in question - Johnson & Johnson's Head-to-Toe Baby Wash, J&J Bedtime Bath, CVS Night-Time Baby Bath, Aveeno Soothing Relief Creamy Wash and Aveeno Wash Shampoo - was needed to produce to positive result.

The researchers have been quick to point out that the soaps don't produce a "high" in any way.