A new article published in StatPearls stated that photosensitivity refers to various symptoms, diseases and conditions (photodermatoses) caused or exacerbated by exposure to sunlight. It is classified into five categories: primary photodermatosis, exogenous photodermatosis, photo-exacerbated dermatoses, metabolic photodermatosis and genetic photodermatosis.

Primary or autoimmune photodermatoses can be of various types:

• Polymorphic light eruption
• Juvenile spring eruption
• Actinic folliculitis
• Actinic prurigo
• Solar urticaria
• Chronic actinic/photosensitivity dermatitis
• Hydroavacciniforme (associated with Epstein-Barr virus)

Types of Exogenous or drug/chemical-induced photodermatoses

• Drug-induced photosensitivity – common photosensitizing drugs are thiazides, tetracyclines, non-steroidal anti-inflammatory drugs (NSAIDs), phenothiazines, voriconazole, quinine and vemurafenib.
• Photocontact dermatitis – occurs due to phototoxic chemicals, such as psoralens in plants, vegetables, fruit; fragrances in cosmetics; sunscreen chemicals; dyes; and disinfectants
• Pseudoporphyria – induced by drugs and/or renal insufficiency

Photo-exacerbated or photo-aggravated dermatoses

The common types are:

• Cutaneous lupus erythematosus (acute, subacute and chronic variants)
• Dermatomyositis
• Sjogren syndrome
• Darier disease
• Rosacea
• Melasma

Less common types are:

• Pemphigus vulgaris
• Pemphigus foliaceus
• Atopic dermatitis
• Seborrheic dermatitis
• Psoriasis
• Lichen planus (actinicus)
• Erythema multiforme
• Mycosis fungoides

Metabolic photodermatoses (rare)

• Porphyria cutaneatarda
• Erythropoietic protoporphyria
• Variegate porphyria
• Erythropoietic porphyria (Gunther disease)

Genetic photodermatoses (very rare disorders due to genomic instability)

• Xeroderma pigmentosum
• Cockayne syndrome
• Trichothiodystrophy
• Bloom syndrome
• Rothmund Thomson syndrome

The etiology of a photodermatosis depends on its classification. Some occur due to autoimmune reactions, drugs, connective tissue diseaseand abnormal inherited biochemical pathways.Photosensitivity may be observed in both males and females at all ages; however, different types of photosensitivity may be prevalent at different times of life. Genetic and environmental are factors associated with photosensitivity.

Photosensitivity is caused by an abnormal reaction to a component of the electromagnetic spectrum of sunlight and a chromophore (reactive compound) within the skin. Patients can be sensitive to one kind of sunlight – for example, only to ultraviolet radiation, ultraviolet A or B (UVA, UVB), or visible light or to a wider range of radiation. The most common photosensitivity is to UVA; exposure to visible light triggers porphyria. Moreover, each category and sub-category of photosensitivity has a unique reaction pattern seen on pathology.

Management of photosensitivity involves sun protection and treatment of the underlying disorder. Photosensitivity reactions can be prevented by careful protection from sun exposure and avoidance of exposure to artificial sources of UVR. There is more ultraviolet radiation in the tropics compared to temperate areas; in the Southern hemisphere compared to the Northern; during summer compared to winter; at high altitude compared to sea level; and in the middle of the day compared to the extremes of the day.

Prevention Strategies entail:

• Avoiding exposure to direct sunlight
• Staying indoors and seeking shade when outdoors
• Dressing up in covering clothing and wearing a wide-brimmed hat when outdoors.
• Use of a broad-spectrum sunscreen SPF 50 or higher, covering all exposed skin. Sunscreen should protect from UVB and UVA and be water resistant. It should be applied generously and reapplied every two hours while outdoors.

Interestingly, the primary photodermatosis polymorphic light eruption can be treated by graduated, and cautious, exposure to ultraviolet radiation.

Source: StatPearls [Internet]. August 10, 2020.