Babies in Europe have been developing hypertrichosis, more commonly known as werewolf syndrome, after their parents used an anti-baldness medication.

The Pharmacovigilance Center of Navarre (CFN) in Spain discovered that 11 babies recently developed werewolf syndrome, linked to a caregiver’s use of minoxidil, Spanish newspaper El País reported.

Minoxidil is a medication approved by the U.S. Food and Drug Administration (FDA) that can be sold without a prescription to adults experiencing age-related hair loss.

Werewolf syndrome, or hypertrichosis, is a condition where excessive hair grows in unwanted places.

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The CFN was informed of a case of werewolf syndrome in April 2023, in which a baby boy had gradually developed hair growth on his back, legs and thighs over the course of two months.

The scientists discovered that his father, who had been off work for a month looking after him, had been using a 5-percent minoxidil lotion on his scalp to treat baldness.

When the baby was no longer exposed to this drug, his excess hair went away and he was fine, the CFN said. However, very young babies exposed to minoxidil may be at risk of damage to their heart and kidneys.

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After analyzing the April 2023 case, the CFN searched through the Spanish Pharmacovigilance System and the European Medicines Agency’s EudraVigilance databases and found 10 other recent cases of werewolf syndrome linked to minoxidil in Europe.

In all of these cases, symptoms went away after the parent stopped taking minoxidil, but the CFN’s information bulletin maintained that it was still a serious situation.