Dermatitis

Photosensitivity dermatitis

Created 2008.

Learning objectives

  • Identify and manage photosensitivity dermatitis

Introduction

Photosensitivity dermatitis is the name given to an eczematous eruption arising in response to exposure to electromagnetic radiation. It is most commonly provoked by exposure to sunlight. The reaction may relate to UVB, UVA and/or visible light. It arises in all skin types.

Photosensitivity dermatitis has several causes.

  • Contact photoirritant or photoallergic dermatitis
  • Photosensitivity eruptions due to drugs
  • Photoaggravated atopic dermatitis
  • Idiopathic chronic photosensitivity dermatitis

Clinical features of photosensitivity

Photosensitivity eruptions affect the exposed areas. Most often, these are the following sites.

  • Face: sparing behind ears, under nose, eyelids, hairline (make-up may be protective)
  • Neck: sparing the anterior portion under the chin and including a V on the anterior chest
  • Dorsum of hands: sparing finger webs
  • Forearms: sharp cut-off at cuff level
  • Feet: dorsum of feet, sparing strap marks from sandals

Contact photoirritant or photoallergic dermatitis
The chemicals that cause irritant reactions may also cause allergic reactions.

In general an irritant or toxic reaction is sunburn-like and results in deep pigmentation; an allergic reaction is more likely to resemble acute or chronic dermatitis. However, as both types of reaction may arise from the same substances, repeated or chronic eruptions are best distinguished by patch testing. Exposing duplicate sets of patches to UVA is known as photopatch testing. It is non-standardised but allergen sets are available. The most frequent photoirritants and photoallergens are:

  • Psoralens (in plants, phytophotodermatitis)
  • Antiseptics (e.g. in antibacterial soaps)
  • Tar products (take care in using tar and UVA for phototherapy)
  • Fragrances (berloque dermatitis)
  • Sunscreens (less frequent today as lower concentrations used and PABA is avoided)
Phototoxic dermatitis

Photosensitivity eruptions due to drugs
Drugs can cause photosensitivity by toxic and allergic mechanisms.

A toxic, or sunburn-like reaction is most likely with:

  • Tetracyclines
  • Nonsteroidal anti-inflammatory drugs
  • Retinoids
  • Methoxsalen (used for photochemotherapy)
  • Chlorpromazine

The most common drugs implicated in the development of an allergic reaction are:

  • Hydrochlorthiazide
  • Sulphonylureas
  • Quinine
Drug-induced photosensitivity reactions

Photoaggravated atopic dermatitis
Some patients with atopic dermatitis become photosensitive. As they already have a chronic dermatitis the diagnosis of photosensitivity is often delayed. Photosensitivity can be extremely severe.

Photoaggravated atopic dermatitis

Chronic photosensitivity dermatitis
Chronic photosensitivity dermatitis is a rare disease. It most often affects elderly men . They have severely itchy thickened dry skin in all areas exposed to the sun throughout the year, especially the face, neck and backs of hands. In skin biopsies of longstanding cases the histology resembles a cutaneous T-cell lymphoma or reticulosis, so chronic photosensitivity dermatitis may also be called actinic reticuloid.

The rash can be provoked by as little as 30 seconds exposure to daylight, with reactions to UVB, UVA and in severe cases to visible light. In some cases it is preceded by contact allergy (especially to plants such as chrysanthemum ) or contact photoallergy or photosensitivity reaction to a drug (when it is also called persistent light reaction). Treatment with systemic steroids and strong immune suppressive medications such as azathioprine is usually necessary.

Chronic photosensitivity dermatitis

Investigations in photosensitivity

Patch testing should be carried out in chronic photosensitivity reactions. It is negative in most patients with atopic dermatitis but there are often contact allergies in those with idiopathic chronic photosensitivity dermatitis.

Photopatch tests are similar to patch tests. Two sets of perfumes, antiseptics, plant materials and sunscreens may be applied. After removal, one set is exposed to a small dose of ultraviolet radiation (UVA) (5 J/cm2). Positive allergic responses are classified as follows:

  • Contact allergy: Reaction to allergen exposed to light equal to unexposed site
  • Contact photoaggravation: Reaction to allergen exposed to light greater to unexposed site
  • Contact photoallergy: Reaction to allergen exposed to light but no reaction to unexposed allergen

Phototests involve exposing the skin to graduated doses of broadband and/or monochromatic ultraviolet radiation to confirm the presence of a systemic photosensitivity.

Photoprovocation tests involve three repeated daily doses of one and a half minimal erythema doses of broadband ultraviolet radiation in an attempt to reproduce a specific photodermatosis.

Skin biopsies and laboratory investigations, such as antinuclear antibody (ANA) panels and porphyrin profiles, may be required to further confirm the diagnosis.

Differential diagnosis of photosensitivity

Photosensitivity dermatitis may be confused with other forms of photosensitivity:

  • Polymorphic light eruption (PMLE): grouped papules arising within hours of sun exposure and disappearing within days
  • Actinic prurigo: chronic childhood prurigo more evident on exposed sites. Chelitis is characteristic.
  • Hyroa vacciniforme: rare blistering eruption of childhood.
  • Solar urticaria: rare acquired wealing reaction to exposure to ultraviolet radiation.
  • Porphyrias: inherited or acquired photosensitivity due to accumulated photosensitising porphyrins in skin and blood (porphyria cutanea tarda and erythropoeitic protoporphyria are the most common types).
  • Photoexacerbated dermatoses e.g. cutaneous lupus erythematosus, pellagra
Photosensitivity disorders

The differential diagnosis of photosensitivity dermatitis also includes airborne contact dermatitis. In such cases, only the exposed skin may be affected but there is no sparing in creases, behind the ears, or of shadowed sites such as under the chin.

Management of photosensitivity

Management depends on the specific skin condition. Contact with known allergens should be avoided and photosensitising drugs stopped if possible. Eczematous reactions are treated with emollients and topical steroids.

Photoprotective measures should include:

  • Staying indoors during the middle of the day.
  • Wearing a broadbrimmed hat and fully covering and densely woven clothing.
  • Broad spectrum sunscreens, applied liberally and frequently to areas that are not covered up.
  • Oral photoprotective medications such as Polypodium leucotomas or antioxidants.

Severe dermatitis may require oral corticosteroids or immunosuppressive agents, especially azathioprine.

Activity

Compile a comprehensive list of the drugs you commonly prescribe that may cause photosensitivity.

See smartphone apps to check your skin.
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Related information

References:

On DermNet NZ:

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