Dermoscopy is nowadays the most utilized tool to evaluate patients complaining hair loss or nail disease.
Trichoscopy refers to dermoscopy of hair and scalp and permits to study hair shafts, follicular ostia, scalp skin, and blood vessels. Trichoscopy allows to evaluate several basic parameters such as the density, the diameter, hair shaft diversity, as well as the presence/absence of follicular ostia, the scalp vessels changes and other signs of hair disorders. Trichoscopy also helps clinician to predict the activity of the disease and to evaluate the response to treatments. A further use of trichoscopy is to guide the choice of the appropriate site for scalp biopsy in cases needing a histopathological evaluation.

Onychoscopy, or nail dermoscopy, was initially suggested for the assessment of nail melanocytic lesions, but it use has gradually been extended to the evaluation of all nail dystrophies, becoming a routine diagnostic instrument. In daily practice, onychoscopy is used to reinforce presumptive clinical diagnoses, as well as to guide the management of different nail diseases. In most cases nail dermoscopy only permits a better visualization of symptoms already evident to the naked eye.
However, in a few diseases, the technique can provide important diagnostic information. Nail dermoscopy can study all visible parts of the nail unit, but can also be utilized to observe the nail matrix, the only non-visible nail epithelium, in conjunction with intra-operative methods.

A correct trichoscopy or onychoscopy assessment of the patient requires a good knowledge of both the technique and the physiology of hair and nails.
This masterclass is aimed to provide the necessary knowledge and hail and nail physiology that allows good comprehension of the trichoscopy and onychoscopy signs. Understanding the pathophysiology of the different dermoscopy sign will then allow easy diagnosis and management of the diseases of skin appendages.