Polymorphous light eruption (PLE) presents with itchy red small bumps on sun-exposed skin, particularly face, neck, forearms and legs.

[3] It is a non-life-threatening and potentially distressing[4] skin condition that is triggered by sunlight and artificial UV exposure[5] in a genetically susceptible person,[6] particularly in temperate climates during the spring and early summer.

[4] Treatments include prevention with sun avoidance and supervised light therapy, and symptom control with topical steroids.

[11] 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.

[2] The rash may persist for many days to a couple of weeks,[5] resolving spontaneously without scarring as long as further sunlight exposure is avoided.

[2] However, the "hardening" effect, with respite during the later summer, frequently occurs with gradual exposure of sunlight,[5] eventually leading to significant improvement.

[6] It is thought to be due to a type IV delayed-type hypersensitivity to an allergen produced in the body following sunlight exposure,[12] in a genetically susceptible person.

[10] It is also thought that skin microbiome or microbial elements could be involved in pathogenesis of the disease [13][14] 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.

However, positive antinuclear antibody and extractable nuclear antigen (anti-Ro/La) in low titre may be found, even in the absence of other criteria to suggest a diagnosis of lupus erythematosus.

If clinical findings suggest a possibility of porphyria, urinary and red cell porphyrin screening may be performed and are negative in PLE.

[2] When a decision to undertake this is made, a small area of the frequently affected skin is exposed to varying doses of UVA and minimal erythema dose (MED) (amount of UV radiation that will produce minimal redness of skin within a few hours following exposure)[2][17] of broadband UVB for three consecutive days.

[18] Sunlight has been documented to trigger numerous skin conditions and the confusing terminology and categorisation previously has made the correct diagnosis and subsequent treatment difficult.

[16] This includes emotional distress, anxiety and depression[12] Thomas Bateman, following on from findings of his predecessor, Robert Willan,[24] first recorded a description of PLE in the nineteenth century, defining it as eczema solare with recurrent non scarring eczematous lesions triggered by sun exposure.