A male infant presented at 15 weeks of age having developed a number of dark coarse scrotal hairs during the preceding week (fig 1). There were no other signs of androgenisation and testes were of normal infant size. Investigations showed a testosterone concentration within the normal range at 3.2 nmol/l (age related reference range 0.03–6.14 nmol/l),¹ and a normal urinary androgen profile. Serum cortisol, 17 hydroxy-progesterone, FSH, LH, thyroxine, and TSH levels were unremarkable. Subsequent linear growth was normal and by 7 months of age, the scrotal hair had disappeared.

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Figure 1

 Scrotal hair in our 15 week old male infant patient.

Transient isolated scrotal hair development starting at a few months of age has been reported in a total of 10 infants from various centres in the USA.^2–5 To our knowledge this has not been reported from the UK. In seven cases spontaneous disappearance of scrotal hair occurred at between 8–15 months of age.^2,5 In two cases it was “diminished” by 13 months and 21 months of age,⁴ and in the remaining case time of resolution was not stated.³ All were thoroughly investigated and no underlying pathological cause was found.

The appearance of hair in the pubic area in a male infant usually suggests a true excess of circulating androgens, for example in congenital adrenal hyperplasia. However, the development of isolated scrotal hair alone, without other signs of androgenisation, may be a benign phenomenon explained by an increased sensitivity of scrotal hair follicles in affected infants to the normal “physiological” high concentrations of testosterone seen in early infancy.² As concentrations decrease later in infancy the scrotal hair disappears or diminishes. Although this seems to be a benign condition, it should be regarded only as a diagnosis of exclusion—all infants with signs of androgenisation need urgent full investigation.