Photodermatitis

Photodermatitis, sometimes referred to as sun poisoning or photoallergy, is a form of allergic contact dermatitis where the allergen needs to be activated by light to sensitise the allergic response, causing a rash or other systemic effects upon subsequent exposure. Unlike sunburn, photodermatitis involves a more complex immunological reaction.

Signs and Symptoms

Photodermatitis manifests with a range of symptoms that can affect the skin and, occasionally, other body systems. Common symptoms include swelling, difficulty in breathing, a burning sensation, and a red itchy rash that sometimes resembles small blisters. The affected skin may peel, and individuals might experience nausea. Persistent itching can lead to blotches, which may develop an unsightly orange to brown tint, particularly near or on the face.

Causes

Photodermatitis can result from a variety of medications and substances that increase sensitivity to sunlight. These include:

• Medications: Sulfa drugs (e.g., certain antibiotics, diuretics, COX-2 inhibitors, and diabetes drugs), tetracycline antibiotics (e.g., doxycycline, minocycline), and some NSAIDs (e.g., ibuprofen, naproxen sodium).
• Chemicals and compounds: Psoralens, coal tars, photo-active dyes (eosin, acridine orange), musk ambrette, methylcoumarin, lemon oil, PABA (in sunscreens), oxybenzone (UVA and UVB blocker in sunscreens), salicylanilide (industrial cleaners), St John's wort, hexachlorophene (in prescription antibacterial soaps), benzoyl peroxide, and retinoids (e.g., isotretinoin).
• Other conditions: Pellagra, a deficiency of Vitamin B3.

Photodermatitis can also be triggered by certain plants, such as Ammi majus, parsnip, giant hogweed (Heracleum mantegazzianum), common rue (Ruta graveolens), and Dictamnus albus (burning bush). The condition caused by plant exposure is specifically termed phytophotodermatitis.

Prevention

Preventing photodermatitis primarily involves avoiding exposure to the triggering chemicals or substances. Wearing protective gloves when handling potential allergens and avoiding sunlight exposure are key strategies. Sunscreens with at least SPF 30 and high UVA protection are recommended for affected areas to minimise exposure. Additionally, managing risk factors such as avoiding specific medications or plants known to cause photodermatitis is essential.

Diagnosis and Treatment

Diagnosis typically involves a thorough patient history to identify potential allergens and light exposure. Dermatology and immunology specialists may conduct patch tests to determine specific sensitivities.

Treatment focuses on minimising exposure to the allergen and managing symptoms. Topical corticosteroids, antihistamines, and moisturising creams can help alleviate skin irritation and inflammation. In severe cases, systemic corticosteroids may be prescribed. Addressing any underlying conditions, such as Vitamin B3 deficiency, is also very important in managing the condition effectively.

---

Self-assessment MCQs (single best answer)

What is another term for photodermatitis?

Which of the following is a common symptom of photodermatitis?

Which type of medications can increase sensitivity to sunlight and trigger photodermatitis?

Which of the following plants can cause phytophotodermatitis?

What is a recommended SPF level for sunscreens to prevent photodermatitis?

What deficiency is associated with causing photodermatitis?

Which type of specialist is typically involved in the diagnosis and treatment of photodermatitis?

What is the primary strategy for preventing photodermatitis?

Which topical treatment is commonly used to manage symptoms of photodermatitis?

Which of the following is NOT a cause of photodermatitis?