What Is Polymorphous Light Eruption

  • Ka Yin Chan BSc Cognitive Neuroscience and Psychology, University of Manchester
  • Jasmine Abdy Bachelor of Science - BSc, Medical Microbiology with a Year in Industry, University of Bristol

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Have you ever heard of polymorphous light eruption or have you ever seen anyone that is very sensitive to the sun? If you find yourself or people around you start developing rashes after being under the sun, this article might be able to answer the questions in your head!

Polymorphous light eruption (PMLE) is a skin condition that occurs when your skin is exposed to the sun, a rash would appear on that part of the skin. It is usually itchy. Sometimes it also appears as red bumps depending on the severity of the condition.

Interested in knowing more about PMLE? Continue reading this article!


Definition of polymorphous light eruption (PMLE)

Polymorphous Light Eruption, commonly abbreviated as PMLE, is a skin condition that appears as a rash and itches or develops into small red bumps on the skin that has been exposed to the sun. It is also described as sun poisoning since PMLE is strongly associated with exposure to sunlight, particularly ultraviolet (UV) light. It has a prevalence of about 20%. 


Itchy rash

One of the primary and most distressing symptoms of PMLE is the development of an intensely itchy rash. Sometimes, it only takes a few hours for an itchy or burning rash to appear after being exposed to the sunlight. However, some may find themselves getting the rash up to 2 to 3 days after sun exposure depending on the person. It can last up to 2 weeks. It will commonly not leave any scarring after recovery. The rash usually appears on body parts that are exposed to the sun, such as the head, neck, chest and arms but the face is often not affected. 

Small bumps

PMLE often presents as the formation of small red bumps or vesicles on the skin. These bumps contribute to the overall redness and textural irregularities observed in the affected areas. The appearance of these lesions may be alarming for individuals experiencing PMLE, further emphasising the need for accurate diagnosis and appropriate management.

Papules and plaques

The rash associated with PMLE exhibits a polymorphic nature, appearing in various forms such as papules and plaques. Papules are small, raised areas on the skin, while plaques are larger, flat lesions. This diversity in presentation adds complexity to the clinical picture of PMLE, making it crucial for healthcare professionals to recognize these variations during diagnosis.


Although the underlying mechanism of PMLE is still uncertain, there have been various causes suggesting to be associated with PMLE. 

Abnormal immune system response

The primary cause of Polymorphous Light Eruption (PMLE) is believed to be an abnormal immune system response to ultraviolet (UV) radiation. When susceptible individuals are exposed to sunlight, particularly UVB and UVA rays, their immune system reacts exaggeratedly, developing characteristic skin lesions. This immune response involves a complex interplay of cellular and molecular mechanisms that are not yet fully understood.

The immune system normally protects the body from harmful invaders, but in PMLE, it appears to misinterpret sunlight as a threat, leading to an inflammatory response in the skin. This abnormal reaction manifests as an itchy rash, small bumps, and other skin symptoms associated with PMLE.

More common in individuals with fair skin

There is evidence to suggest a genetic predisposition to PMLE. Individuals with a family history of PMLE may be more prone to developing the condition. Specific genetic factors that influence how the immune system responds to UV radiation and regulates inflammatory processes are areas of ongoing research. Understanding the genetic basis of PMLE may contribute to identifying individuals at higher risk and inform potential preventive measures.

Occurs in spring or early summer

The seasonal occurrence of PMLE, often in the spring or early summer, points to a connection with changing sunlight patterns. During these seasons, individuals are exposed to higher levels of UV radiation after a period of reduced sun exposure in the winter. The skin, having adapted to lower UV levels, may react abnormally when suddenly exposed to increased sunlight. This seasonal aspect emphasises the importance of preventive measures during times of elevated sun intensity.

Ultraviolet radiation intensity

The intensity of ultraviolet radiation plays a crucial role in triggering PMLE. UVB radiation, in particular, is associated with the development of PMLE lesions. The intensity of UV radiation varies with geographical location, altitude, and time of day. Individuals living in regions with high UV levels may be more susceptible to PMLE, necessitating greater vigilance in sun protection.

Hormonal influences

There is some evidence to suggest that hormonal changes may influence the development of PMLE as it is more common for women to have PMLE than men. For example, hormonal fluctuations associated with the menstrual cycle or pregnancy may affect the skin's response to sunlight. Further research is needed to fully understand the role of hormones in PMLE development.

Medications and chemicals

Certain medications and chemicals can increase the skin's sensitivity to sunlight, potentially exacerbating PMLE symptoms. Photosensitising medications, such as certain antibiotics, nonsteroidal anti-inflammatory drugs (NSAIDs), and diuretics, may contribute to the development or worsening of PMLE. Healthcare professionals need to consider medication history when evaluating individuals with PMLE.

Immune system modulation

Conditions or treatments that modulate the immune system, such as autoimmune diseases or immunosuppressive therapies, may impact the likelihood of developing PMLE. The intricate relationship between the immune system and sunlight exposure suggests that factors affecting immune function can influence PMLE susceptibility.


Although PMLE cannot be cured, there are several ways to avoid it and improve the conditions. 

Sun avoidance

The cornerstone of managing Polymorphous Light Eruption (PMLE) is sun avoidance. Individuals with PMLE should take proactive measures to minimise direct sunlight exposure, especially during peak hours when ultraviolet (UV) radiation is most intense. Seeking shade, wearing protective clothing (such as wide-brimmed hats and long-sleeved shirts), and using umbrellas can help create a physical barrier between the skin and sunlight.

Sunscreen application

Regular and liberal application of broad-spectrum sunscreen with a high Sun Protection Factor (SPF) is essential in preventing PMLE symptoms. Sunscreen should be applied to all exposed skin areas, even on overcast days, and reapplied every two hours or more frequently if swimming or sweating. Choosing a sunscreen that protects against both UVA and UVB rays is crucial for comprehensive sun protection.

Protective clothing

Wearing protective clothing serves as an additional layer of defence against UV radiation. Lightweight, long-sleeved shirts, pants, and wide-brimmed hats can effectively shield the skin from direct sunlight. Specialised sun-protective clothing with an ultraviolet protection factor (UPF) rating can offer enhanced sun protection.

Topical steroids

For individuals with persistent or severe symptoms, healthcare professionals may prescribe topical corticosteroids. These medications help reduce inflammation and alleviate itching associated with PMLE. It's important to use topical steroids as directed by a healthcare provider, as prolonged or excessive use can lead to side effects.


Over-the-counter or prescription antihistamines can be effective in managing the itching associated with PMLE. These medications work by blocking histamine, a compound released during an allergic or inflammatory response. Antihistamines can help alleviate itching and improve overall comfort during PMLE flare-ups.

Moisturisers and emollients

Regular use of moisturisers and emollients can help soothe the skin and reduce dryness associated with PMLE. Keeping the skin well-hydrated may contribute to overall skin health and resilience.


In some cases, controlled exposure to UV light in a medical setting, a process known as phototherapy or photo hardening, may be recommended. This involves gradually increasing the skin's tolerance to UV radiation in a controlled environment, potentially reducing the likelihood of PMLE reactions upon subsequent sun exposure. Phototherapy is typically administered under the supervision of a dermatologist.

Immune modulators

In certain situations, immune-modulating medications may be considered for individuals with severe or recurrent PMLE. These medications, such as systemic corticosteroids or immunosuppressive drugs, work to modify the immune system's response and reduce inflammation. However, the use of these medications is generally reserved for more challenging cases and requires careful monitoring due to potential side effects.

Lifestyle adjustments

Making lifestyle adjustments can contribute to overall PMLE management. This may include planning outdoor activities during off-peak sunlight hours, using car window tints or UV-protective films, and being vigilant about sun protection measures even on cloudy days.

Consultation with a dermatologist

Individuals experiencing PMLE symptoms, especially if they are severe or recurrent, should seek consultation with a dermatologist. A dermatologist can provide an accurate diagnosis, tailor treatment plans to individual needs, and offer guidance on preventive measures. Regular follow-ups with a dermatologist may be necessary to monitor progress and make adjustments to the treatment plan as needed.


In a nutshell, PMLE is a skin condition that causes an itchy or burning rash on the parts of the skin that have been exposed to the sun. The underlying cause is still unknown and therefore there is no known cure. However, there are many ways to avoid PMLE or to improve the symptoms. It is very important to go to a doctor for professional advice if you suspect you are getting PMLE.


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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Ka Yin Chan

BSc Cognitive Neuroscience and Psychology, University of Manchester

She is a Neuroscience student with strong interest in clinical research and medical communications. She believes that the ever-growing field of scientific research is crucial for understanding health and hence improve it.

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