Photoallergic eczema – causes, symptoms and treatment

Photoallergic eczema is an inflammation of the skin caused by the combined action of photoallergen and ultraviolet radiation with a wavelength of 320 to 400 nm (UVA). The assessment of the frequency of photoallergy in the population varies. Data proving such hypersensitivity in 6-8% of respondents prevail, although some authors estimate it at as much as 22%.

What are the causes of photoallergic eczema?

The causative agents of photoallergic eczema include topical chemicals and substances of general use. The locally active ones include:

  1. halogenated salicylanilides,
  2. preservatives and disinfectants,
  3. sunscreens,
  4. fragrances (musk ambret, cinnamaldehyde),
  5. plant protection products (especially thiocarbamates), d
  6. animal feed additives,
  7. plants (phytophotodermatitis)

In addition, photoallergic eczema can occur after general application:

  1. non-steroidal anti-inflammatory drugs,
  2. sulfonamides,
  3. phenothiazine and benzodiazepine derivatives,
  4. tricyclic antidepressants.

Cross-reactions between thimerosal – a preservative of vaccines, immune serums, eye drops, ears, nose, contact lens solutions, some cosmetics – and piroxicam are quite common.

The mechanism of photoallergic eczema

As a result of the interaction of the allergen and UV radiation (absorption spectrum), a modified substance is formed – happedwhich binds to skin proteins to form photoallergen, which in turn stimulates the immune response. During the subsequent interaction of the UV radiation (trigger spectrum) and the allergen in the skin, delayed hypersensitivity reactions and clinical symptoms of contact eczema occur.

Photoallergic eczema – symptoms

The lesions are located on the exposed parts of the body in the case of external contact with the allergen. The skin of the triangle under the chin remains unchanged and there is a sharp distinction between the inflammatory changes and the healthy skin covered with clothing. The skin lesions may be more widespread in people allergic to systemic medications.

The patient develops:

  1. erythema spots,
  2. lumps
  3. bubbles
  4. sometimes blisters
  5. severe itching of the skin, limited to places exposed to sunlight.

Lack of proper diagnosis and constant exposure to the allergen can lead to the development of chronic photoallergic dermatitis, with lichenification and the spread of lesions to the skin not exposed to sunlight.

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Diagnostics of photoallergic eczema

Initially, there is intercellular edema of the epidermis and perivascular lymphocytic infiltrates, and then acanthosis and parakeratosis occur.

In the diagnostics of photosensitivity with the use of exogenous photosensitizing substances, contact phototests with chemical compounds with recognized photosensitizing action (ready-made commercial kits) or with substances suspected of such action are necessary in establishing the diagnosis. The materials used for the patch phototests are used on the skin of the back in a double set, one of which is irradiated and the other is used to control. Typically the UVA dose ranges from 5 to 10 J / cm2.

It is sometimes difficult to distinguish photoallergic from phototoxic reactions. Sometimes photoallergic eczema has to be differentiated from atopic eczema. The results of the phototests are helpful in recognition.

Treatment of photoallergic eczema

In the treatment of ailments, it is important to avoid contact with photoallergens and to use preparations with UVA filters and ointments with the addition of corticosteroids.

Lit .: [1] Kieć-Świerczyńska M., Kręcisz B .: Skin diseases caused by photosensitivity. Med Pr 2001, 52; 383-87. [2] Roelandts R .: The diagnosis of photosensitivity. Arch Dermatol 2000; 136-1152.

Source: A. Kaszuba, Z. Adamski: “Lexicon of dermatology”; XNUMXst edition, Czelej Publishing House

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