What Is Polymorphic Light Eruption?

Polymorphic light eruption is the most common type of skin response in people who are sensitive to sunlight and other types of ultraviolet (UV) light. It causes a reddish skin rash that forms hours to days after exposure to direct sunlight. The rash can differ from person to person and take many forms.

This problem affects up to 20% of people, though it is most often found in young women in temperate climates. It affects 4 times more women than men. People of all races and skin types can have this disease.

Having family members with this disease increases your risk of getting it. Treatment involves oral and topical drugs to relieve skin problems. The main approach to disease control is prevention. Avoiding direct sunlight and using sunscreen daily are advised. Phototherapy (light therapy) may be used in severe cases.

This article describes polymorphic light eruption symptoms, causes, diagnosis, and treatment.

Types of Polymorphic Light Eruption

Polymorphic light eruption is one of many types of photodermatoses, a group of disorders that trigger an abnormal skin reaction to UV light.

Photodermatoses can be categorized as either primary or secondary diseases, though there is no standardized system of classification. The skin reacts to electromagnetic radiation in primary types of photodermatoses, including infrared light, UV light, and sunlight. In secondary diseases, the reaction is often a feature of a systemic disease (one affecting the entire body rather than a particular area) that is induced by sunlight.

Polymorphic light eruption is classified as a primary type of photodermatosis. Subtypes of polymorphic light eruption include the following variants:

• Juvenile spring eruption: This is an eruption of papules and vesicles on the helix or outer rim of the ear. It usually affects boys and young male adults in the springtime, often after sunny and cold spring days.
• Polymorphic light eruption sine eruption: Polymorphic light eruption sine eruption is a flare of pruritus, or itchy skin, on sun-exposed skin without visible changes to the affected area.
  

Polymorphic Light Eruption Symptoms

Polymorphic light eruption symptoms occur as different types of rashes, hence the name "poly" (many) "morphic" (forms). The onset of symptoms occurs in females between the ages of 20 and 40 in about 75% of cases, though they can begin in early childhood or late adulthood as well.

Symptoms appear as red and itchy skin lesions of various types that include the following forms:

• Papules (solid, raised lesion)
• Macules (flat, discolored lesions)
• Plaque (raised patches)
• Erythema multiforme (red, patchy lesions)
• Prurigo strophulus (lesions resembling insect bites)
• Vesicles (fluid-filled blister)

Fever, headaches, and malaise may occur, though they are not commonly linked to the disease.

The first sign of polymorphic light eruption usually appears after an affected person has their first exposure to intense sunlight. This often occurs in the early spring or early summer in moderate climates.

Symptoms of polymorphic light eruption appear from several hours to days after exposure to light. While the face is rarely affected, the rash can occur in the following areas:

• Décolletage (the bust)
• Forearms
• Backs of hands
• Lower legs
• Feet

Is Polymorphic Light Eruption an Autoimmune Disease?

The exact cause of polymorphic light eruption isn't fully understood, though it is considered an autoimmune disease.

Research suggests that the rash occurs as a delayed hypersensitivity reaction to an antigen that exists in your skin cells. People with this condition have immune cells triggered by exposure to natural sunlight or artificial sources of ultraviolet (UV) radiation. The reaction causes a skin rash.

Genetics seems to contribute to the development of this condition. A positive family history is present in 10% to 63% of cases.

Diagnosis

Diagnosis of polymorphic light eruption can be challenging because rashes can appear as a symptom of many conditions. A physical examination, a family history, and your timeline of sun exposure are often used to exclude other disorders related to sun exposure.

Your healthcare provider may use the following tests to complete a diagnosis of polymorphic light eruption:

• Skin biopsy (removing a sample of skin for analysis in a lab)
• Blood test
• Photo testing, which involves exposure of your skin to UV light to recreate the problem)
• Porphyria urine test (tests for a buildup of chemicals that produce red blood cell proteins in the body)

Treatment

Treatment for polymorphic light eruption varies based on the severity of the disease symptoms and general patient condition. Therapies are preventive or suppressive.

The most common treatments include the following:

Sunscreen Application and Sun Avoidance

Mild cases of polymorphic light eruption respond well to the following preventive strategies:

• Avoid sun exposure between the times of 11 a.m. and 3 p.m. when UV light is the strongest.
• Use broad-spectrum sunscreens with UVA (ultraviolet A) protection capacity.
• Wear protective clothing when in situations that might provoke the condition.

Oral and Topical Medications

Eruptions can be treated with topical corticosteroids to reduce symptoms, treat itching, and shorten the duration of the rash.

A short course of oral prednisone is sometimes used to treat occasional severe attacks. Other medications have also been used to treat symptoms:

• Azathioprine and cyclosporine
• Hydroxychloroquine
• Beta carotene
• Nicotinamide
• Omega‐3 polyunsaturated fatty acids
• Topical antioxidants
• Escherichia coli (E. coli) filtrate
• Thalidomide

Phototherapy

Phototherapy is the primary treatment used for severe cases of polymorphic light eruption. This treatment involves the application of UVA or UVB (ultraviolet B) light to the skin. It can be effective when administered as a preventive measure in early spring to promote skin tolerance or hardening of the skin to sunlight.

Prognosis

The prognosis for polymorphic light eruption may improve over time.

The reaction tends to recur annually. It can persist throughout the year for some patients who are closest to the equator. However, the condition often diminishes in severity with age, resulting in a relatively lower prevalence of polymorphic light eruption over time.

For most people, the reactions caused by the disease are mild and self-limiting. Only about 26% of people with polymorphic light eruption seek medical attention.

Coping

Limiting your exposure to UV light can significantly help you manage symptoms of the disease. This is especially effective during the first one or two times you are exposed to the sun in the early spring.

When symptoms occur, limiting sun exposure can help rashes clear, and symptoms calm faster. Consult your healthcare provider for the treatments most appropriate for your symptoms when they arise. If you have a severe form of the disease, consider phototherapy to build UV light tolerance prior to the spring and summer.

While the disease may not impact your physical well-being, don't ignore feelings of frustration and despair that symptoms may trigger. Living with a chronic condition is a risk factor for depression.

Summary

Polymorphic light eruption is a skin reaction that appears after exposure to direct sunlight or other forms of UV light. The problem takes many forms, though it often appears as a red, itchy rash on areas exposed to the sun, except for the face. The rash can take many forms.

Up to 20% of people live with this problem. It affects women more often than men. While the rash can cause pain and embarrassment, the majority of people affected do not seek medical treatment for the problem. The rashes usually disappear on their own without scarring.

The cause of the disease is unknown, though it may be genetic and tends to run in families. Treatment includes preventing the onset of rashes with less sun exposure. Topical and oral drugs can help relieve symptoms. Phototherapy may help promote sun tolerance.

Most people have fewer rashes by the end of the summer season. Symptoms also lessen with age.

A Word From Verywell

Following practical tips to limit sun exposure can help reduce your risk of developing rashes common with polymorphic light eruption. Applying sunscreen regularly on exposed areas of your skin can also reduce symptoms.

Some of the greatest challenges with this condition may be emotional. Limiting your daytime activities based on sun exposure can leave you feeling isolated, while the appearance of red, inflamed rashes can affect your self-confidence.

Although the rashes that occur with polymorphic light eruption don't cause scarring and occur less often with age, seeking help for the physical effects of this condition can improve your emotional well-being.