Numerous physical and chemical factors, usually associated with improper hair care and styling, may cause changes in the structure of the hair shaft. Other changes can appear as a result of unknown endogenous factors. The most important structural abnormalities include: ringed, twisted, fleecy, moniliform, bamboo and knotty hair. Furthermore, this group also comprises knotty and longitudinal hair splitting, trichoschisis and trichothiodystrophy. These disorders are characterized by thin, breakable, matt, brittle and dry hair. Such abnormalities are more often observed in women, especially those with fair hair. Mechanical damage is the most common reason for these disorders. Damage may result from excessive and improper combing and brushing, perming, cutting with blunt tools, straightening, using hair dryers, brushes or curlers with too hot stream of air, intense operation of solar beams, too tight plaits, hair lightening and dyeing, bathing in salty water, and scratching or pulling hair due to a scalp disease. The changes most often affect the hair of the head. Avoiding mechanical damage enables the regeneration of normal hair. Many of these disorders are resistant to treatment with the use of vitamin preparations.