Exogen hair characterization in human scalp

The study from 17 years ago focused on identifying and characterizing exogen hair, which is the shedding phase of hair, from the human scalp. It involved 23 volunteers and used a non-invasive method involving silicon-based polymers and a calibrated dynamometer to sample exogen hair. The researchers found that exogen hair is passively retained and lacks cellular elements of the outer root sheaths, unlike telogen hair. The method developed did not affect other hair cycle stages and typically found less than seven exogen hairs per cm² in normal individuals. Additionally, the study showed that exogen hair is thinner and can be exhausted with repeated sampling, with the first sampling accounting for over half of the total exogen hair. One male subject with a high number of exogen hairs suggested an early stage of androgenetic alopecia. The study concluded that exogen is a distinct phase of the hair cycle and the sampling method is specific for this stage, which could be useful in future hair loss research.