Pili annulati: electron histochemical studies on affected hairs.

In this study we have shown that in pili annulati all the normal layers within each cuticle cell are present, and show a normal distribution of cystine. The presence of well ordered macrofibrils, composed of microfibrils embedded in a cystine rich matrix, in both regions of the hair shaft indicates that normal keratinization can and does take place. We have demonstrated the presence of electron-opaque, cystine positive material at the intermacrofibrillar spaces and suggest that the presence of the cortical holes is in part due to insufficient cortical material to occupy the space available, and in part due to the dissolution of the intermacrofibrillar material, possibly by water of other chemical agents, diffusing through an apparently more permeable cuticle.