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

Introduction

Approximately 50% of women will experience hair loss during their lives. The most common cause is the androgenetic alopecia (AGA), or female pattern hair loss, which primarily affects genetically predisposed women aged 12–40 years. It causes the shrinking of terminal follicles in the frontal and parietal scalp areas [1]. Other less common hair loss disorders include alopecia areata, telogen effluvium, cicatricial alopecia, and traction alopecias from harsh hair styling [2]. Hormonal imbalances from polycystic ovarian syndrome (PCOS), thyroid problems, and other endocrine disorders can also contribute to hair loss [3]. Additionally, deficiencies in essential nutrients such as iron and zinc can exacerbate hair loss [4]. Originally developed as an oral medication for high blood pressure, Minoxidil is now used topically to slow or stop hair loss and promote regrowth. This vasodilator, available in 2% and 5% concentrations, promotes the growth and darkening of body hair. Minoxidil opens potassium channels, hyperpolarizing cell membranes and enhancing vascular dilation, which improves nutrient delivery to follicles, thus promoting hair cycle progression from the resting to growth phase [5]. PRP involves extracting a patient’s own blood, processing it to enrich for platelets, and reinjecting it into the scalp, which can stimulate dormant hair follicles [6]. Head covering is a common cultural and religious practice among many women, including those of Jewish, Muslim, and African descent, who frequently wear wigs, veils, or bonnets as part of their daily routines [7]. Understanding how these practices interact with dermatological treatments is essential, as illustrated in the following case report, which explores the unexpected effects of scalp occlusion on minoxidil absorption and its clinical consequences.

Case Report

A 28-year-old patient suffering from congenital deafness with no genetic cause, was not following any specific treatment and had no allergies. She managed an African hair salon, did not engage in sports, and did not use tobacco, alcohol, or drugs. The clinical examination revealed a fronto-parietal median alopecia extending to the vertex (Figure 1). There were no signs of scalp trouble (eg, infection, parasites, dandruff). Blood tests detected mild anemia (10 g/dl) with a ferritin level of 15 ng/mL, a low vitamin D level at 28 nmol/L, and a normal TSH (0.67 mlU/L). The treatment started with dietary supplements such as biotin (Bepanthene), zinc, and vitamin D, along with local treatment using 5% minoxidil spray twice daily (6 sprays per application). Additionally, PRP injections into the scalp, followed by 15 minutes of LED therapy (light-emitting diode), has been initiated with 1 session per month for 3 months. After 2 months of treatment, she noticed increased hair growth on her face, arms, and legs (Figure 2). She also mentioned experiencing eye swelling in the morning upon waking up.

Discussion

Given this specific clinical presentation and the onset of hirsutism, several hypotheses were proposed. Was it a complication of the PRP or the minoxidil? A literature search validated the hypothesis of minoxidil overdose (Table 1). Hypertrichosis, characterized by excessive hair growth, can arise from various factors, including genetic conditions, environmental influences, and medical treatments [8,9]. This hirsutism caused by minoxidil overdose condition was previously described in the case of a 26-year-old woman who developed generalized hypertrichosis after using a 5% topical solution for alopecia areata [10]. In clinical trials involving 1333 females, 4% of participants had minoxidil-induced hypertrichosis [11]. The FDA-approved safe upper limit for topical minoxidil application is 1 mL twice daily (approximately 6 sprays per application) [12]. Exceeding this dose does not improve efficacy but significantly increases the risk of systemic absorption and adverse effects [13]. Some authors reported cases of severe hypertrichosis in infants whose parents were using 5–7% topical minoxidil, suggesting that transdermal exposure via skin-to-skin contact or fomites may contribute to unintended systemic effects [14,15]. Further discussion with the patient revealed to the physician that her alopecia was causing significant psychological distress, leading her to wear a wig during the day. At night, she wore a cap to protect her hair, all while applying 5% minoxidil twice daily. The patient’s scalp was constantly occluded, day and night. This resulted in much greater penetration of minoxidil into the scalp than with regular application, leading to systemic absorption of the product and subsequent development of hirsutism and hypertrichosis. Minoxidil exerts its effects by opening ATP-sensitive potassium (K[ATP]) channels, specifically the SUR2 subtype [16]. This action relaxes vascular smooth muscle and increases blood flow to the hair follicles. In the context of hair growth, this increased blood flow provides the necessary oxygen and nutrients for hair follicle cells, promoting hair growth. However, overactivation of these channels can lead to excessive hair growth, contributing to hypertrichosis [17]. After discovering this cause, discontinuation of minoxidil was recommended, and a course of laser hair removal treatment was carried out with 5 sessions, spaced 1 month apart each time. She also practiced dermaplaning (shaving) of her face during this period (Figure 3). The origin of this alopecia is likely mixed: traction alopecia due to hairstyles with African braids, especially in the frontal area, combined with AGA (androgenetic alopecia), explaining the hair fragility and parietal alopecia. Minoxidil is an effective treatment (Figure 4) but can occasionally lead to hypertrichosis, especially when applied in high concentrations or over large areas of the body.

Conclusions

This case illustrates the critical need for precise patient instruction on the correct application of topical therapies to prevent adverse systemic effects such as hypertrichosis. It further underscores the necessity for clinicians to account for cultural practices, such as head covering. Many women of Jewish and Muslim faiths commonly cover their hair with wigs, veils, or head coverings. Similarly, in Africa, it is common to wear a wig or bonnet at night [7,18]. These insights clarify how patient behavior and treatment application affect clinical outcomes, offering key lessons for improving patient care and education in dermatology. For androgenetic alopecia in women, 2% minoxidil is recommended twice daily or 5% foam once daily to reduce the risk of facial hypertrichosis while ensuring efficacy.