Polymorphous light eruption (PMLE) is a common photosensitivity disorder characterized by an abnormal skin reaction to ultraviolet (UV) radiation, typically following sun exposure. It most commonly affects young adult women and individuals living in temperate climates. Unlike sunburn, PMLE is an immunologic reaction that does not require intense sun exposure to be triggered.
The term “polymorphous” reflects the variety of lesion types it can produce, including papules, plaques, and vesicles, which may vary in size and distribution. The condition is non-contagious and tends to recur in a seasonal pattern, particularly during spring and early summer.
Causes and Pathophysiology of PMLE
The exact cause of PMLE remains unclear, but it is believed to result from an abnormal immune response to compounds in the skin that are altered by UV exposure.
Underlying Mechanism:
- Exposure to UVA or UVB radiation alters skin proteins.
- These altered proteins are recognized as antigens by the immune system.
- The immune system mounts a delayed hypersensitivity reaction, causing inflammation and skin lesions.
Risk Factors:
- Genetic predisposition
- Fair skin types (Fitzpatrick I–III)
- Living in areas with long winters and intense spring sunlight
- Female gender (2:1 ratio compared to males)
Recognizing the Symptoms of Polymorphous Light Eruption
PMLE typically presents within hours to days of sun exposure and resolves spontaneously over several days without scarring. The clinical presentation varies widely between individuals.
Common PMLE Symptoms:
- Red, itchy rash on sun-exposed areas (neck, arms, chest, legs)
- Papules, plaques, or vesicles with symmetrical distribution
- Burning or stinging sensation
- No involvement of the face in many cases (helps differentiate from lupus)
- Recurrence annually in spring or early summer
- Lesions subside without pigmentary changes or scarring
Diagnosis of PMLE
PMLE is typically diagnosed clinically through a thorough medical history and physical examination. Diagnostic confirmation may be considered when the diagnosis is uncertain or when autoimmune conditions are suspected.
Diagnostic Tools:
- Phototesting: Controlled UV exposure to replicate lesions
- Skin biopsy: Shows lymphocytic perivascular infiltrate, helpful to exclude other dermatoses
- Antinuclear antibody (ANA) test: To rule out lupus erythematosus
- Photoprovocation tests: Used in specialized centers to confirm photosensitivity
Differential Diagnoses:
- Lupus erythematosus
- Solar urticaria
- Actinic prurigo
- Photoallergic or phototoxic drug reactions
Effective Treatment Options for Polymorphous Light Eruption
PMLE can often be managed effectively with a combination of preventive strategies, topical therapies, and systemic medications when necessary.
1. Sun Protection
- Daily use of broad-spectrum sunscreen (SPF 30+ with UVA/UVB protection)
- Protective clothing: Wide-brimmed hats, long sleeves, UV-filtering sunglasses
- Avoid peak sunlight hours (10 a.m. to 4 p.m.)
- Gradual sun exposure early in the season to promote natural hardening
2. Topical Treatments
- Corticosteroid creams: Reduce inflammation and control itching
- Calcineurin inhibitors (e.g., tacrolimus): As a steroid-sparing option
3. Systemic Therapies
- Oral antihistamines: Alleviate itching and burning
- Hydroxychloroquine: Used in resistant cases or where autoimmune overlap is suspected
- Oral corticosteroids: Short-term use in severe flare-ups
4. Phototherapy (Desensitization Therapy)
- Administered in early spring under medical supervision
- Gradual exposure to narrowband UVB or PUVA therapy
- Promotes photo-hardening by adapting the skin to sunlight
Preventing PMLE Recurrence
Prevention focuses on limiting UV exposure and improving the skin’s natural tolerance to sunlight.
Key Preventive Measures:
- Start phototherapy before the onset of the sunny season
- Consistent and correct use of sunscreens year-round
- Supplementation with beta-carotene or polypodium leucotomos extract (under professional guidance)
- Awareness and avoidance of photosensitizing agents (e.g., certain perfumes, medications)
Living with Polymorphous Light Eruption
While PMLE can be distressing, especially due to its seasonal nature and visibility, it is benign and non-scarring. Most patients find that their symptoms lessen in severity over time with adequate sun protection and skin conditioning strategies.
Patient Education Tips:
- Educate about safe sun practices and UV index awareness
- Recommend routine skin checks to detect other photodermatoses
- Promote psychological support for patients with recurring flares
Prognosis and Outlook
The long-term outlook for PMLE is favorable. Many individuals experience spontaneous improvement over several years. Persistent cases are manageable with early diagnosis, tailored therapy, and comprehensive lifestyle adjustments.
Polymorphous light eruption is the most prevalent form of idiopathic photodermatosis, presenting as a delayed hypersensitivity reaction to UV radiation. Through strategic sun protection, targeted therapies, and patient education, PMLE symptoms can be effectively controlled, allowing individuals to lead normal lives even in sun-prone environments. Early recognition and proactive care remain central to improving outcomes and preventing unnecessary interventions.
