Hypertrichosis Induced by Minoxidil: A Case of Systemic Absorption from Scalp Occlusion.

BACKGROUND Minoxidil is a widely used topical treatment for hair loss, but improper use can lead to systemic absorption and unintended adverse effects such as hypertrichosis. Identifying risk factors for increased absorption is crucial to prevent adverse reactions. CASE REPORT We report the case of a 28-year-old woman with androgenetic and traction alopecia, treated with 5% minoxidil spray twice daily, platelet-rich plasma (PRP) therapy, and LED treatment. After 2 months, she experienced significant hair regrowth but also developed excessive hair growth on her face, arms, and legs, along with morning periorbital swelling. Further investigation revealed that she wore a wig during the day and a tight night cap, creating continuous scalp occlusion, which likely increased systemic absorption of minoxidil. Given these findings, minoxidil was discontinued, and the patient underwent laser hair removal, with a gradual resolution of hypertrichosis. CONCLUSIONS This case underscores the importance of proper patient education regarding minoxidil application techniques to prevent excessive systemic absorption and hypertrichosis. Patients should be advised to avoid excessive application, prolonged occlusion, and high doses, as these factors may elevate the risk of systemic effects. Clinicians should consider scalp occlusion as a potential contributor to hypertrichosis in patients using topical minoxidil. Further studies are warranted to investigate the role of absorption-enhancing factors in minoxidil-related adverse effects.