In addition, it may occur in other parts of the body in some people treated for inflammatory skin diseases with phototherapy.The rash is usually quite symmetrical and characteristic for each individual, appearing similar with each recurrence, but can look dissimilar in different people.Fever, fatigue and headaches have been previously associated with the eruption, but are rare.The rash may persist for many days to a couple of weeks, resolving spontaneously without scarring as long as further sunlight exposure is avoided.Recurring yearly, the eruption can sometimes last longer than a few days if persistent and repeated sun exposure occurs. However, the "hardening" effect, with respite during the later summer, frequently occurs with gradual exposure of sunlight, eventually leading to significant improvement. Causes
The cause of PLE is not yet understood, but several factors may be involved. It is thought to be due to a type IV delayed-type hypersensitivity to an allergen produced in the body following sunlight exposure, in a genetically susceptible person. It is also thought that skin microbiome or microbial elements could be involved in pathogenesis of the disease

UV exposure
PLE can be provoked by UVA or UVB (chief cause of sunburn) rays, meaning it can be triggered even by sunlight through glass. UV-A is a major constituent of sunlight, can pass through glass, is relatively resistant to sunscreen and can cause light eruption without sunburn.Artificial UV light sources from tanning units and phototherapy treatment units can also trigger PLE.
Polymorphous light eruption (PLE), sometimes also called polymorphic light eruption (PMLE), is a non-life-threatening and potentially distressing skin condition that is triggered by sunlight and artificial UV exposure in a genetically susceptible person, particularly in temperate climates during the spring and early summer. Due to its many clinical appearances, it is named polymorphic or polymorphous and the terms are used interchangeably. The resulting itch can cause significant suffering.PLE is also defined as an idiopathic primary photodermatosis, in which the photosensitizer is unknown.Treatments include prevention with sun avoidance and supervised light therapy, and symptom control with topical steroids. Signs and symptoms
Typically, the first episode develops in the spring following the first exposure to intense sun. Further episodes of the irritable rash occur several hours to days following subsequent sun exposure.PLE appears on areas of the skin newly exposed to sunlight such as the visible part of the neckline, backs of hands, arms and legs, and feet, but less commonly the face. At these areas, there may be feelings of burning and severe itching. Smooth red-topped small papules which merge into plaques, small fluid-filled blisters (papulovesicles) and less commonly target-shaped lesions which look like erythema multiforme may be visible.