A Technique for More Precise Distinction Between Catagen and Telogen Human Hair Follicles Ex Vivo

In the study, researchers developed a technique using methylene blue (MB) staining to distinguish between late catagen and telogen human hair follicles (HFs) ex vivo, which is typically challenging with stereomicroscopic analysis alone. The study involved 800 follicular units (FUs) from 8 Caucasian male patients undergoing hair transplantation, with each patient contributing 100 FUs. The FUs containing catagen and/or telogen HFs were microdissected, stained with MB, and then evaluated. The MB staining improved the visualization of HF structures and allowed for correct hair cycle stage classification in 95.63% of cases, compared to 72.02% accuracy without MB staining. This method facilitates research on human catagen and telogen HFs without resorting to histology. The study also found a higher percentage of catagen HFs (6.7%) compared to telogen HFs (3.6%) in the patients, suggesting that the percentage of scalp telogen HFs may have been previously overestimated in the literature. The authors propose that the distribution of hair stages in healthy human scalp requires systematic re-evaluation.