Hydroa vacciniforme (HV) is a rare, chronic photodermatosis of unknown origin occurring in childhood. Recurrent vesicles on sun-exposed skin that heal with vacciniform or varioliform scarring characterize HV. The histopathologic features are distinctive and demonstrate intraepidermal reticular degeneration and cellular necrosis.  Most cases remit spontaneously by late adolescence.  See the image below.
The etiology of hydroa vacciniforme (HV) is uncertain. HV may be a distinct entity distinguished by scarring or may occur within the spectrum of polymorphous light eruption. Skin lesions occur on sun-exposed skin, such as the face, ears, and hands. There is an association between HV occurrence and latent Epstein-Barr virus (EBV) infection, particularly if necrotic lesions are present.  T cells positive for EBV-encoded small nuclear RNA (EBER) have been detected in the cutaneous infiltrates of some patients with HV. Ultraviolet-induced cutaneous lesions with histopathology consistent with HV have also been shown to contain EBER-positive cells.  In general, the EBV DNA blood load is higher in patients with HV than in patients with other photosensitivity disorders. 
The frequency of HV varies according to country but is estimated to be around 0.34 case per 100,000 people.
Males have a higher incidence of HV than females. Males who are affected may also have a longer course of disease than females. 
HV predominately affects children aged 3-15 years.  The mean duration from onset of symptoms to its resolution is nine years. Resolution of symptoms typically occurs in adolescence or young adulthood, although symptoms persist throughout life in some patients.  Cases of HV in infants and elderly persons have also been described. 
The prognosis is excellent; hydroa vacciniforme (HV) typically remits by adolescence. No mortality is associated with classic HV.
Patients are advised regarding strict sun avoidance, frequent application of high SPF sunscreens with UV-A blocking agents, and protective clothing.
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