Laugier-Hunziker syndrome (LHS) was initially described in 1970 as acquired, benign hyperpigmented macules of the lips and buccal mucosa frequently associated with longitudinal melanonychia. Extended mucocutaneous features have been observed since that original description, including macular pigmentation of the genitalia. No underlying systemic abnormalities are associated with Laugier-Hunziker syndrome, and no malignant predisposition exists. This lack of somatic abnormalities has moved some authorities to propose a name change to Laugier and Hunziker pigmentation.  When associated with nonclassic body locations or atypical features, the name idiopathic lenticular mucocutaneous hyperpigmentation has been used. 
The etiology of melanosis in Laugier-Hunziker syndrome is unknown. A lack of family members with Laugier-Hunziker syndrome is characteristic in most cases. To date, only one case of familial Laugier-Hunziker syndrome has been described, which involved a mother and 2 daughters.  Environmental risk factors have not been identified.
The incidence is rare, but it is likely underreported. White patients and those of Latino descent have been described in the United States.
The prevalence appears to be higher in France and Italy when compared with the United Kingdom and the United States. Worldwide, approximately 60 cases were reported from 1970-1991. Among the patients described prior to 1989, 27 (93%) of 29 patients were from continental Europe. To date, more than 100 cases have been described. 
Laugier-Hunziker syndrome mainly affects whites; however, persons of Hispanic, Arabic, or Asian  descent have been described.
Idiopathic buccal melanosis without longitudinal melanonychia is a normal finding in 38% of black patients and in 5% of white patients. Physiologic melanoplakia, a term also used to describe idiopathic racial or ethnic melanosis, is most commonly noted on the gingiva of individuals with darker skin types. The histopathologic features of Laugier-Hunziker syndrome are indistinguishable from those of physiologic melanoplakia.
Longitudinal melanonychia (also known as melanonychia striata) without associated mucosal melanotic macules is a normal finding in 77% of blacks by age 20 years, and it is seen in 90% of blacks by the fifth decade of life. It most commonly occurs on the thumbs, with onset often during infancy or puberty.
Laugier-Hunziker syndrome was initially predominantly thought to affect females, with an estimated female-to-male ratio of 2:1.  However, the idea that Laugier-Hunziker syndrome is equally distributed between the sexes is gaining popularity. 
Essential melanotic pigmentation typically develops during early to middle adulthood, in persons aged 20-40 years, but it can occur as late as the sixth or seventh decade of life. A mean age of 52 years  and a median age of 42 years  have been reported.
Physiologic (racial or ethnic) melanosis characteristically occurs during the first 3 decades of life.
Peutz-Jeghers syndrome (PJS), a major differential diagnosis of Laugier-Hunziker syndrome, usually has its onset at birth or during the first few years of life. However, sporadic cases of PJS have been reported in as many as 40% of cases, and it can have a late onset. See Peutz-Jeghers Syndrome for more information on this syndrome.
Laugier-Hunziker syndrome has a benign course. One report has described spontaneous remission.  Systemic illness and malignancy are not features of Laugier-Hunziker syndrome. Such findings in association with mucocutaneous melanotic hyperpigmentation exclude the diagnosis of Laugier-Hunziker syndrome.