Indirect Exposure to Topical Minoxidil Causing Generalized Hypertrichosis in Children: A Report of Two Cases

Topical minoxidil is widely prescribed for androgenetic alopecia and is generally regarded as safe. Hypertrichosis is a recognized adverse effect, most commonly localized to the site of application or adjacent areas. In contrast, generalized hypertrichosis resulting from indirect exposure is rare and occurs predominantly in infants and young children [1, 2]. We report two Egyptian pediatric cases of generalized hypertrichosis resulting from indirect exposure through skin contact, highlighting this uncommon but clinically significant phenomenon. The first case (Figure 1) involved a 2-year-old child who presented with progressive, diffuse, excessive hair growth involving the face, trunk, and extremities over several weeks. The child was otherwise healthy, with normal growth and development, no behavioral abnormalities, and no history of systemic disease or medication use. Physical examination revealed generalized terminal hair growth sparing mucosal surfaces. Laboratory investigations, including thyroid and adrenal function tests, were within normal limits. A detailed history revealed that a parent had been using a topical 5% minoxidil solution for androgenetic alopecia and frequently shared close physical contact and bedding with the child shortly after application. There was no evidence of direct application. The parent was advised to avoid any accidental exposure of the child to the hair treatment medication. Nine months after cessation of minoxidil exposure and implementation of preventive measures, gradual and marked regression of hypertrichosis was observed during follow-up. The second case (Figure 2) involved a 7-month-old infant who developed widespread excessive hair growth on the face, trunk, and limbs over 3 months. The infant was otherwise healthy, with normal growth and development. There was no medical condition, and he was not receiving any medications. Further inquiry identified chronic indirect skin exposure to topical minoxidil from a caregiver, including frequent skin-to-skin contact and shared sleeping surfaces. No behavioral, systemic, or endocrine abnormalities were identified. The caregiver was advised to avoid any further exposure of the child to minoxidil. Six months after the caregiver discontinued minoxidil and avoided further exposure, excessive hair growth progressively diminished to near-complete resolution. Generalized hypertrichosis induced by topical minoxidil is uncommon and appears to affect pediatric patients disproportionately. Increased susceptibility in this population is likely related to thinner skin, a higher body surface area–to–weight ratio, and enhanced percutaneous absorption [2, 3]. Systemic exposure may occur through skin contact, contaminated bedding or towels, or residual drug on caregivers' hands or clothing, even without direct application. Minoxidil promotes hair growth by prolonging the anagen phase and enhancing follicular vascularization; when absorbed systemically, these effects may lead to diffuse hair growth beyond the scalp [4]. The differential diagnosis of generalized hypertrichosis in children includes genetic syndromes, endocrine disorders, metabolic conditions, and medication-induced causes [2]. In both cases, the absence of systemic findings, normal routine investigations, and a clear temporal relationship with minoxidil exposure strongly supported a drug-induced etiology. Previous reports indicate that minoxidil-induced hypertrichosis in children is benign and reversible, consistent with our observations [3, 5]. These cases underscore the importance of obtaining a detailed exposure history when evaluating pediatric hypertrichosis. Increased clinician awareness and appropriate counseling of caregivers about topical minoxidil are essential to prevent inadvertent exposure and unnecessary diagnostic investigations. The authors have nothing to report. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.