Trichorrhexis Nodosa

Trichorrhexis Nodosa.

Possibly the most frequent cause of hair shaft severance.  Swellings (nodes) develop along the hair shaft’s axis – seen as highlighted spots on the micrograph below.
Node disintegration (immediate / eventual) reveals the brush like macro fibrils of the cortex (trichoclasis). Severance is inevitable.

Trichorrhexis Nodosa
micrograph x 50  © B J Stevens 

Possible genetic inspiration (autosomal dominant trait).
A number of syndromic forms have been described.

Oxidative chemistry which reduces cystine levels.
Sea bathing and sunlight (Papa et al. 1972).
Hair straightening chemistry (Jolly  & Carpenter 1967).
High temperature thermal styling.