The children – some of them babies – began growing hair all over their body after being given what was thought to be omeprazole, a drug that helps with gastric reflux.

After investigating, authorities discovered the treatment actually contained minoxidil, a medication used for the treatment of hair loss.

The health minister, Maria Luisa Carcedo, said on Wednesday they found that the bad batches came from a laboratory that had “put this medication [minoxidil] in a container that was marked omeprazole” and distributed it to pharmacies as such.

The children are now suffering from the rare condition known as hypertrichosis, which causes abnormal hair growth.

It is unclear how the laboratory FarmaQuimica Sur, a supplier of active ingredients and pharmaceuticals based in the southern city of Malaga, made the mistake, which emerged in June.

A health ministry spokesman said the 17 children affected so far were in the northern region of Cantabria, Andalusia in the south and Valencia in the east.

In a statement, the ministry said the condition was expected to reverse after the children stopped taking the drug, which has been withdrawn from the market.

Carcedo said the laboratory had been closed as a precaution.

A spokeswoman for Andalusia’s health department said the four affected children in the southern region – three babies and a seven-year-old – were doing well.