Polymorphous light eruption, also known as polymorphic light eruption, is an itchy rash caused by sun exposure in people who have developed a sensitivity to sunlight (photosensitivity). The rash usually appears as red, tiny bumps or slightly raised patches of skin.
Polymorphous light eruption occurs most often during spring and early summer when a person's exposure to sunlight increases. Repeat episodes are less likely as the summer progresses, but polymorphous light eruption often recurs each year after the first incident.
Although polymorphous light eruption usually goes away on its own without treatment, medications may be needed to treat severe or persistent cases. Measures to protect the skin from sun exposure or light therapy may help prevent recurring episodes of polymorphous light eruption.
The term "eruption" refers to the rash, which usually appears within minutes to hours — or sometimes within a couple of days — after exposure to sunlight. The rash usually appears on areas of the body that tend to be covered during winter but exposed in summer: the upper chest, front of the neck and the arms.
Characteristics of the rash may include:
- Dense clusters of small bumps
- Raised rough patches
- Itching or burning
- Blistering and swelling (less common)
Rarely people may have other signs or symptoms, such as fever, chills, headache or nausea. These conditions may be the result of an associated sunburn rather than polymorphous light eruption.
When to see a doctor
See your doctor if:
- You have any rash with no obvious cause, such as a known allergy or known exposure to poison ivy
A number of conditions — including some serious diseases — can cause skin rashes with similar appearances. It's important to get a prompt diagnosis and appropriate treatment.
Seek immediate medical care if your rash is:
- Accompanied by fever
The exact cause of polymorphous light eruption isn't well-understood. The rash appears in people who have developed a sensitivity to components of sunlight, and in particular ultraviolet (UV) radiation from the sun or other sources, such as tanning beds or tanning lamps. This sensitivity is referred to as photosensitivity. Photosensitivity results in sunlight-induced immune system activity that produces inflammation and a rash.
UV radiation is a wavelength of sunlight in a range too short for the human eye to see. UV light that reaches the earth is divided into two wavelength bands — ultraviolet A (UVA) and ultraviolet B (UVB).
A person with photosensitivity can react to both types of UV radiation. Although UVB doesn't penetrate glass, UVA does. Therefore, exposure to sunlight through windows may cause a reaction in some people with photosensitivity.
Sensitivity to sunlight lessens with repeated exposure in polymorphous light eruption. Therefore, there are somewhat predictable features of polymorphous light eruption:
- An episode is most likely to occur after the first one or two exposures to sunlight after a long period of no exposure. This usually means that an episode occurs during the spring or early summer or during a winter vacation in a sunnier location.
- Episodes are less likely to occur as the summer progresses.
- After the first episode of polymorphous light eruption, additional episodes are likely to recur on an annual basis each spring or early summer.
- Some people gradually become less sensitive over several years and eventually may no longer experience recurring episodes.
Although anyone can develop polymorphous light eruption, several factors are associated with an increased risk of the condition:
- Women are more likely to develop the disorder.
- The first episode most often appears during the teenage years or 20s.
- People with fair skin or those living in northern regions are more likely to develop the disorder.
- A family history of polymorphous light eruption among some people with the condition suggests a possible genetic risk factor.
You're likely to start by seeing your family doctor or primary care doctor, but you may be referred to a specialist in skin diseases (dermatologist).
Because appointments can be brief, and because there's often a lot of ground to cover, it's a good idea to arrive well-prepared. Here's some information to help you get ready for your appointment, and what to expect from your doctor.
What you can do
- Be aware of any pre-appointment restrictions. At the time you make the appointment, be sure to ask if there's anything you need to do in advance.
- Write down any symptoms you're experiencing, including any that may seem unrelated to the reason for which you scheduled the appointment.
- Write down key personal information, including any major stresses or recent life changes.
- Make a list of all medications, vitamins or supplements that you're taking.
- Write down questions to ask your doctor.
Your time with your doctor is limited, so preparing a list of questions can help you make the most of your time together. For polymorphous light eruption, some basic questions to ask your doctor include:
- What's the most likely cause of my symptoms?
- What kinds of tests do I need? Do these tests require any special preparation?
- Is this condition temporary or long lasting?
- What treatments are available, and which do you recommend?
- What types of side effects can I expect from treatment?
- Are there any restrictions that I need to follow?
- Is there a generic alternative to the medicine you're prescribing me?
- Are there any brochures or other printed material that I can take home with me? What websites do you recommend visiting?
What to expect from your doctor
Your doctor will ask you a number of questions about your symptoms and your medical history. Be prepared to answer the following:
- When did the rash appear?
- Does it itch or cause pain?
- Have you had a fever associated with the rash?
- Do you have any other symptoms?
- What prescription drugs, over-the-counter medications or dietary supplements do you take? What is the dosage of each?
- Did you recently start a new medication?
- Have you recently used a cosmetic or fragrance in the area of the rash?
- Have you had a similar rash before? When?
- Has the duration of your sunlight exposure increased recently?
- Have you recently used a tanning bed or lamp?
- Do you use sunscreen?
What you can do in the meantime
Avoid sun exposure whenever possible. If you can't avoid the sun, use a broad-spectrum sunscreen with an SPF of at least 15. Apply sunscreen generously, and reapply every two hours — or more often if you're swimming or perspiring.
Your doctor can probably make a diagnosis of polymorphous light eruption based on a physical exam and your answers to questions. Laboratory tests may be needed to confirm a diagnosis or rule out other conditions.
Your doctor will do an exam to check your general health. In particular, he or she will examine the rash and the condition of your skin at other sites.
Your doctor may order one of the following tests if a diagnosis isn't certain, the rash doesn't resolve at an expected rate, or there is any reason to suspect another condition causing the rash. Tests may include:
- Skin biopsy. Your doctor may scrape a tiny portion of the rash to remove a sample of tissue (biopsy) for examination in a lab. The biopsy is primarily used to rule out other conditions that may be causing a rash.
- Blood tests. A nurse or assistant may draw blood for laboratory tests that can rule out other conditions.
- Phototesting. You may be referred to a dermatologist for phototesting. During the test small areas of your skin are exposed to measured amounts of UVA and UVB light to try to reproduce the problem. If your skin reacts to the UV radiation, you're considered sensitive to sunlight (photosensitive) and may have polymorphous light eruption or another light-induced disorder.
Other light-induced conditions
Your doctor may need to rule out other disorders characterized by light-induced skin reactions. These conditions include:
- Chemical photosensitivity. A number of chemicals — drugs, medicated lotions, fragrances, plant products — can induce photosensitivity. When this occurs, your skin reacts each time it's exposed to sunlight after ingesting or coming into contact with a particular chemical.
- Solar urticaria. Solar urticaria is a sun-induced allergic reaction that produces hives — raised, red, itchy welts of various sizes that appear and disappear on your skin. The welts can appear within a few minutes of sun exposure and last for a few minutes to hours. Solar urticaria is a chronic condition that can last for years.
- Lupus rash. Lupus is an inflammatory disorder that affects a number of body systems. One symptom is the appearance of a discolored, bumpy rash on areas of skin exposed to sunlight, such as the face, neck or upper chest.
Polymorphous light eruption treatment usually isn't necessary because the rash typically goes away on its own within a few days to a week or more.
- Anti-itch cream. Your doctor may recommend an over-the-counter anti-itch cream, such as a cream containing at least 1 percent hydrocortisone. If you're experiencing severe itch or pain, your doctor may prescribe a more potent corticosteroid cream.
- Pain relievers. An over-the-counter pain medication may help reduce redness, itchiness or pain. These include ibuprofen (Advil, Motrin IB, others), acetaminophen (Tylenol, others) and naproxen sodium (Aleve, others).
Your doctor may suggest light therapy (phototherapy) to prevent seasonal episodes of polymorphous light eruption. Phototherapy exposes your skin to small doses of UVA or UVB light, which helps your skin be less sensitive to light — essentially a controlled version of the increased exposure you would experience over the course of the summer.
One type of light therapy called psoralen plus ultraviolet A (PUVA) combines UVA with administration of a medicine called psoralen, which makes the skin more sensitive to this light. Short-term side effects of this therapy may include nausea, headache and itching.
Self-care measures that may lessen itching related to polymorphous light eruption include:
- Using cold compresses. Apply a towel dampened with cool tap water to the affected skin, or take a cool bath.
- Leaving blisters alone. To speed healing and avoid infection, leave blisters intact. If needed, you can lightly cover blisters with gauze.
To lessen the likelihood of recurring episodes of polymorphous light eruption, take the following precautions:
- Avoid the sun between 10 a.m. and 3 p.m. Because the sun's rays are most intense during this time, try to schedule outdoor activities for other times of the day.
- Use sunscreen. Fifteen to 30 minutes before going outdoors, apply a broad-spectrum sunscreen, one that provides protection from both UVA and UVB light. Use a sunscreen with a sun protection factor (SPF) of at least 15. Apply sunscreen generously, and reapply every two hours — or more often if you're swimming or perspiring. If you're using a spray sunscreen, be sure to cover the entire area completely.
- Cover up. For protection from the sun, wear tightly woven clothing that covers your arms and legs and a broad-brimmed hat, which provides more protection than does a baseball cap or golf visor. You might also consider wearing clothing designed to provide sun protection. An ultraviolet protection factor (UPF) of 40 to 50 provides the best protection. Follow care instructions on the label of UV-blocking clothes to maintain their protective feature.