Is Minoxidil, the cause of the werewolf syndrome detected in several babies?

A baby unusually covered in long body hair recently alarmed the pharmacovigilance center of Navarre, in Spain. According to a Spanish investigation, this is not an isolated case, with ten other newborns also presenting the werewolf syndrome being identified over the past year. Also known as hypertrichosis, this disorder is characterized by a excessive and unusual growth of hair on the body. This hairiness can appear in a generalized or localized manner, and is often localized on the face and back. Hypertrichosis can be congenital, that is, linked to genetic mutations affecting hair follicles, or acquired, in response to certain medications, diseases, or hormonal imbalances.

The werewolf syndrome detected in babies in Spain has been categorized as acquired. Unlike the congenital form, these infants were not born with this condition but developed abnormal hair growth in the months following their birth.

To shed light on this mystery, the pharmacovigilance center conducted a study and noted that all fathers of newborns suffering from werewolf syndrome had used a lotion containing 5% minoxidil. Developed in the 1970s to treat high blood pressure due to its vasodilating properties, minoxidil is a drug capable of stimulating hair and fur growth. Indeed, this molecule can increase blood flow to hair follicles and seems capable of prolonging the anagen phase, the hair growth phase. Minoxidil is thus sometimes prescribed to people suffering from alopecia.

However, like any medication, minoxidil is capable of causing side effects. Among those listed on the patient information leaflet, we find the risk of distant hypertrichosis, which corresponds to an increase in hair growth in areas far from the application of minoxidil. This is a well-documented phenomenon that only concerns the users of the medication. However, since the werewolf syndrome was detected in Spanish babies, the European Medicines Agency has modified the patient information leaflet for minoxidil and added that there is a risk of hypertrichosis following contact with a person using this medication.

In Spanish babies, two hypotheses emerge to explain the transmission of minoxidil from fathers: affectionate skin-to-skin contact or accidental oral exposure. Indeed, the thin and sensitive skin of infants acts like an open door, easily absorbing this medication. Although its overall structure is the same as that of an adult and is composed of an epidermis, a dermis, and a hypodermis, the epidermis of newborns is 20% thinner than that of adults. Thus, a simple hug can be enough for minoxidil to end up on the babies' skin and be absorbed into their system.

It's worth noting that minoxidil-induced hypertrichosis in infants, caused by their parents' use of the product, is not a new phenomenon. The scientific literature reports similar cases, and these Spanish babies are not the first to be affected by the so-called werewolf syndrome. This was notably observed in a two-year-old child in 2013 and an eight-month-old infant in 2020. Fortunately, this effect is reversible. Indeed, after the fathers stopped using minoxidil, the abnormal hair growth in the Spanish newborns gradually disappeared, as has been previously reported in the scientific literature.

To avoid incidents, it is crucial to exercise caution when using minoxidil around young children and to adopt the correct practices. Therefore, after each application, it is essential to wash your hands thoroughly to remove any residual traces of minoxidil. It is also recommended to wait until the product has completely dried before holding and cuddling an infant. Moreover, if your child is a bit older and capable of moving around the house, it is best to store the minoxidil bottle out of their reach, preferably at a height. Lastly, in case of doubt or the appearance of unusual symptoms in a baby, the best course of action is to promptly consult a healthcare professional.