The failure behavior of the anchorage of hairs during slow extraction

Treatment of excessive hair growth is an important issue in both dermatolog ical and cosmetic practice. In contrast to treatments with medication, most physical methods are treatments that focus on the hair follicle. To obtain insight in the failure behavior of the anchorage of hairs, hairs were extr acted (in vitro) from pig skin at a speed of 0.1 mm/s, one at a time. The p ulling force and tweezers displacement were recorded. The extracted hairs w ere classified with respect to the phase in the growing cycle: anagen (grow ing phase), telogen (resting phase) or other (catagen phase or unable to de termine). The anagen hairs showed a different relation between the tweezers displacement and the pulling force than the telogen hairs. Moreover, the m aximum force that could be applied before a hair was extracted proved to be lower for anagen hairs than for telogen hairs (0.36 N, 1.8 N, respectively ). The extracted hair length, defined as the part of the hair that had been embedded in the skin which was extracted, was higher for anagen hairs than for telogen hairs (4.8 mm, 3.0 mm, respectively). Removing proximal skin t issue and the embedded parts of the anagen hair (root) resulted in a change of the extraction curves. The results indicate that two phenomena play a r ole in the anchorage of anagen hairs. We have proposed a model for the extr action of an anagen hair that has been based on these results: first the in terface between hair and skill that is located around the inner root sheath (IRS) starts to fail, followed by failing of the hair itself in the region where the hair keratinizes. (C) 2001 Elsevier Science Ltd. All rights rese rved.