From the Guidelines
Sun allergy, also known as photosensitivity or photodermatosis, is a condition where the skin reacts abnormally to sunlight exposure, causing a rash or other skin symptoms, with the most common form being polymorphous light eruption (PMLE) as reported in the British Journal of Dermatology 1.
Definition and Causes
Sun allergy is characterized by an abnormal skin reaction to sunlight, resulting in symptoms such as red, itchy bumps or small blisters on sun-exposed skin. This condition occurs when UV radiation triggers an immune response in sensitive individuals, causing the body to treat sun-altered skin proteins as foreign substances. According to the British Journal of Dermatology, polymorphous light eruption (PMLE) is the most common form of sun allergy, with symptoms typically appearing within hours of sun exposure 1.
Risk Factors
People with fair skin, those with certain medical conditions, or individuals taking photosensitizing medications are at higher risk for developing sun allergies. The British Journal of Dermatology reports that the risk of provoking PMLE is high, particularly with the first few PUVA exposures, with at least one episode induced during 12–50% of PUVA treatment courses 1.
Treatment
Treatment for sun allergy typically involves avoiding sun exposure, especially between 10 AM and 4 PM, wearing protective clothing, and using broad-spectrum sunscreen with SPF 30 or higher. For mild symptoms, over-the-counter antihistamines like cetirizine (10mg daily) or diphenhydramine (25-50mg every 4-6 hours) can help reduce itching, while topical corticosteroids like hydrocortisone 1% cream applied 2-3 times daily for up to a week can reduce inflammation. Severe cases may require prescription medications such as oral corticosteroids or phototherapy, with the British Journal of Dermatology reporting the use of PUVA with topical corticosteroid cover and inpatient supervision in UV-protected rooms 1.
Management
To prevent provocation, oral prednisolone (40–50 mg) can be administered for the first 2 weeks of phototherapy, while routine prophylactic application of a potent topical steroid after each exposure in UVB phototherapy can also be effective 1. Post-treatment advice generally includes continued natural sunlight exposure, ranging from 2 h weekly to ‘cautious exposure, with sunscreens for extended outdoor stay’ to ‘expose freely to sun’. The British Journal of Dermatology reports that successful use of ciclosporin, despite concerns about increasing risks of carcinogenesis using it with PUVA, at 5 mg/kg daily in combination with PUVA and initial prednisolone cover, has also been reported in case reports 1.
From the Research
Definition of Sun Allergy
- Sun allergy, also known as solar urticaria, is a rare type of inducible urticaria characterized by wheal and erythema formation shortly after exposure to sunlight or to an artificial light source 2.
- It is a type of photoallergic dermatosis, which is a skin lesion that occurs after sun exposure, characterized by the activation of immunological mechanisms, involving photosensitizers and photoallergens 3.
Causes and Triggers
- The exact cause of sun allergy is not yet entirely understood, but it is believed to be related to the activation of photosensitizers and photoallergens in the skin 3.
- Common photoallergens that can trigger sun allergy include sulfonamide antibiotics, phenothiazines, and halogenated salicylanilides 3.
- Sun exposure, particularly to ultraviolet A (UVA) and visible light, can trigger sun allergy 2, 4.
Symptoms and Diagnosis
- Symptoms of sun allergy include erythema, whealing, and/or pruritus occurring minutes after sun exposure 2, 4.
- Diagnosis is typically made through a combination of clinical history, physical examination, and photo-provocation tests to ultraviolet A (UVA), visible light, and/or UVB 4.
Treatment and Management
- Treatment for sun allergy typically involves avoidance of sun exposure and the use of antihistamines and leukotriene receptor antagonists 2, 4.
- Topical corticosteroids may also be used to treat sunburn and other skin reactions, but their effectiveness is limited and depends on the timing and potency of the corticosteroid 5, 6.