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Prevalence is unknown.

Onset is usually between ages 3 months and 12 years. Hair becomes progressively silvery-blond or straw-colored, dry and disordered, standing out from the scalp and growing in different directions, and being unmanageable to comb it flat. The quantity of hair stays normal. Microscopic analysis reveals a longitudinal groove of the hair shaft with a triangular or kidney-shaped section. The anomaly is clinically detectable when approximately 50% of hairs are affected. Several conditions have been reported to occur with UHS such as ectodermal dysplasia, retinal dysplasia, retinal pigmentary dystrophy, juvenile cataract, digit abnormalities, tooth enamel anomalies, oligodontia, phalango-epiphyseal dysplasia, alopecia areata, atopic eczema, and ichthyosis vulgaris.

The stiffness and brightness of hair are supposed to result from a misshapen dermal papilla inducing an anomaly in the keratinization of the inner root sheath.

Diagnosis relies on clinical and microscopic observation, but electron microscopic analysis of hair shaft can eliminate other hair anomalies.

Differential diagnosis includes Rapp-Hodgkin ectodermal dysplasia, loose anagen hair syndrome, ectrodactyly, cleft/lip palate syndrome, familial tricho-odonto-onchyial ectodermal dysplasia with syndactyly and other ectodermal dysplasias.

UHS is likely to be an autosomal dominant inherited disease with a variable penetrance but no causal gene has been identified yet.

UHS spontaneously regresses in late childhood and only gentle care including conditioners, soft brushes and avoidance of harsh treatments cares of the hair are recommended. Biotin treatment as been used in several patients and might be useful to control nail fragility, leading to acclaimed increase in hair growth after 4 months of supplementation.