Could Minoxidil be responsible for the werewolf syndrome detected in several babies?

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

The werewolf syndrome detected in babies in Spain has been categorised 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 centre conducted an investigation 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 appears capable of extending 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 amended 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 is worth noting that hypertrichosis in infants, induced by the minoxidil used by their parents, is not a new phenomenon. The scientific literature reports similar cases, and these Spanish babies are not the first to be affected by the werewolf syndrome. This was notably observed in 2013 in a two-year-old child and in 2020 in an eight-month-old infant. Fortunately, this effect is reversible. Indeed, after the cessation of minoxidil use by the fathers, the abnormal hairiness of the Spanish newborns gradually disappeared, as had already been reported in the scientific literature.

To avoid mishaps, it is crucial to exercise caution when using minoxidil around young children and to adopt the correct practices. Therefore, after each application, one must not forget to wash their hands thoroughly to remove any residual traces of minoxidil. It is also advisable to wait until the product has completely dried before holding an infant and cuddling them. Furthermore, if your child is a bit older and capable of moving around the house, it is better 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.