More than a dozen children in Spain have been diagnosed with "werewolf syndrome" after an error resulted in medicine used to treat alopecia and hair loss being sold as heartburn medicine for children, according to local media reports from El País and Granada Hoy.

The Spanish Agency of Medicines and Medical Devices confirmed the outbreak of hypertrichosis, commonly known as "werewolf syndrome," to El País Wednesday after 17 cases were reported by parents in three regions in Spain. The disease causes causes excessive hair growth, which some say can make those affected appear like a werewolf.

All the parents of affected children treated their children's heartburn with over-the-counter omeprazole, which is commonly sold in the United States as Prilosec.

An investigation by the agency found that one manufacturer in Spain, Farma-Química Sur, was to blame for a labeling mix up that resulted in children accidentally ingesting minoxidil — the active ingredient in Rogaine — according to reports from El País and Granada Hoy.

Children who repeatedly took the incorrectly-labeled omeprazole developed hypertrichosis, causing hair to grow rapidly on babies' forehead, cheeks, arms and legs, according to one mother's account to El País.

Farma-Química Sur has since been prohibited from manufacturing any medication until this incident has been resolved and all affected omeprazole has been recalled, reported El País.

What is 'werewolf syndrome'?

"Werewolf syndrome," also known as hypertrichosis, is the excess production of hair, either in one specific area or all over the body.

It is unclear how hypertrichosis is obtained, but a form of it can be passed down genetically, according to Healthline.

A boy with hypertrichosis in India went viral in February after a video from Barcroft TV showcased his ailment, while the same publication showed a girl in Bangladesh with the same affliction in 2016.

Other cases can be attributed to the misuse of minoxidil, which can be applied topically or consumed orally.

In these cases, "werewolf syndrome" is temporary and will eventually go away after the medicine stops being ingested.