Loose anagen syndrome (LAS) is an autosomal dominant, age-related disorder characterized by the ability to easily and painlessly extract unsheathed anagen hairs from the scalp with a gentle hair pull. The phenotype is heterogeneous with three distinct clinical presentations. To further characterize the phenotype of loose anagen syndrome and its fluctuations over time, a prospective study of eight cases from three families was conducted over a period of 18 months. Patients were examined using standardized hair-pull and hair-pluck protocols. Each of the three different phenotypes of LAS were found to be present in one family. This implies that these phenotypes are variants of a single genotype, modified by environmental or age-related factors. The hair-pluck trichogram from LAS cases consistently showed a high proportion of loose anagen (LA) hairs. In contrast the hair-pull test was found to vary over time with regards to the number of LA hairs that could be extracted. Periods where no hairs could be obtained on hair pull were found. These findings have important implications in the diagnosis of LAS. A single negative hair-pull test does not exclude the diagnosis. If LAS is suspected on clinical grounds, then either a hair-pluck trichogram or serial re-examination by hair pull would be required to exclude the diagnosis.