Age-associated thin hair displays molecular, structural and mechanical characteristic changes

Area of Science:

• Dermatology
• Hair Biology
• Aging Research

Background:

• Hair thinning is a common aspect of aging in both men and women.
• The specific characteristics of age-associated thin hair remain largely uncharacterized.

Purpose of the Study:

• To analyze the multiscale characteristics of thin versus thick hair in Caucasian women over 50.
• To understand the underlying biological processes contributing to age-related hair thinning.

Main Methods:

• Comparative analysis of thin and thick hair shafts from Caucasian women over 50.
• X-ray diffraction to analyze hair cortex composition.
• Assessment of hair ellipticity, cuticle layers, medulla presence, and mechanical properties (rigidity, viscosity, water diffusion).

Main Results:

• Thin hairs showed fewer K35(+)/K38(-) keratinocytes in the cortex compared to thick hairs.
• X-ray diffraction indicated differences in intermediate filament composition between thin and thick hairs.
• Thin hairs were rounder, had fewer cuticle layers, and less frequent medullae.
• Thin hairs exhibited increased rigidity, decreased viscosity, and reduced water diffusion.

Conclusions:

• Age-associated hair thinning involves significant structural and mechanical modifications, not just reduced diameter.
• These changes are likely driven by an "aged hair program" affecting hair follicle differentiation and keratin expression.
• Understanding these modifications is crucial for addressing age-related hair changes.