What are common skin rashes caused by sun exposure?

Common Skin Rashes from Sun Exposure

The most common sun-induced skin rashes are polymorphic light eruption (PLE), phytophotodermatitis, solar urticaria, and chronic actinic dermatitis (CAD), with PLE being the most prevalent immuno-mediated photodermatosis. 1, 2

Primary Photodermatoses

Polymorphic Light Eruption (PLE)

• PLE is the most common sun-induced rash, presenting as itching or burning papules, vesico-papules, plaques, or erythema on sun-exposed areas within hours to days after UV exposure 1, 2
• Typically affects the V-area of the chest, arms, forearms, legs, and upper back, with the face rarely involved 1
• Lesions last several days and resolve within approximately one week without scarring 1
• Represents a delayed hypersensitivity (Type IV allergic) reaction to UV-induced antigens 1, 3
• Occurs in approximately 10-20% of the population based on epidemiological data 2

Solar Urticaria

• Characterized by acute erythema and urticarial wheals appearing within minutes after UV or visible light exposure 2, 3
• Represents a Type I allergic reaction to photoactivated autoantigens 3
• Can severely impair quality of life in severe cases 3
• Lesions typically resolve within hours once out of sunlight 2

Chronic Actinic Dermatitis (CAD)

• Manifests as persistent dermatitis on chronically sun-exposed skin 2
• More common in older individuals with cumulative sun damage 4
• Requires aggressive photoprotection and may need immunosuppressive therapy 2

Phototoxic Reactions

Phytophotodermatitis

• Results from contact with plant-derived furocoumarins or psoralens (found in limes, celery, figs) followed by sun exposure 5
• Commonly known as "margarita burn" when caused by lime juice exposure 5
• Progresses through characteristic stages: erythematous patches → vesicles resembling second-degree burns → hyperpigmentation that persists for weeks to months 5
• Not an allergic reaction but a direct phototoxic effect 5

Drug-Induced Photosensitivity

• Various medications can cause phototoxic or photoallergic reactions when combined with sun exposure 2, 6
• Clinical patterns vary depending on the causative agent 2

Acute Sun Damage

Sunburn

• Acute erythematous response with increased melanin production and keratinocyte apoptosis 6
• Represents direct UV-induced cellular damage rather than an immunologic process 6
• Most intense with UVB exposure during peak hours (10 AM - 4 PM) 4

Critical Diagnostic Considerations

History is paramount for diagnosis: Document timing of rash onset relative to sun exposure, morphology, distribution (sun-exposed vs. covered areas), medication use, and contact with plants or chemicals 5

Key Distinguishing Features:

• Timing: PLE develops hours to days after exposure; solar urticaria within minutes; phytophotodermatitis 24-48 hours post-exposure 1, 2, 5
• Duration: Solar urticaria resolves in hours; PLE in days; phytophotodermatitis hyperpigmentation persists weeks to months 1, 2, 5
• Distribution: Phytophotodermatitis shows bizarre linear or drip patterns; PLE spares habitually exposed areas like the face 1, 5

Prevention Strategies

All patients with photodermatoses require comprehensive photoprotection 4:

• Minimize sun exposure during peak UV hours (10 AM - 4 PM, especially 11 AM - 1 PM) 4
• Use broad-spectrum sunscreens with SPF ≥15 providing both UVA and UVB protection 4
• Wear protective clothing with tight weave, darker colors, and wide-brimmed hats (>3-inch brim) 4
• Avoid artificial UV sources including tanning beds, which are carcinogenic 4

Common Pitfalls

• Do not confuse PLE with contact dermatitis: PLE strictly follows sun exposure patterns and spares covered areas 1, 5
• Recognize that cloud cover provides minimal protection: 80% of UV rays penetrate light clouds 4
• Remember reflective surfaces intensify exposure: Water, sand, snow, and pavement increase UV radiation reaching the skin 4
• Fair-skinned individuals with red/blond hair who burn easily face highest risk for all photodermatoses 4