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Therapeutics in Dermatology
A reference textbook in dermatology

Photosensitization

14 June 2019, by PINTO A. I.

1 - ACKNOWLEDGEMENTS

Chapter written with the help of the EADV, the Fondation René Touraine and the Therapeutics in Dermatology

2 - OVERVIEW

Photosensitization consists of anomalous reactions resulting from skin exposure to sunlight, responsible for various symptoms and diseases called photodermatoses. It may also occur following indoor exposure to artificial sources of radiation like fluorescent lamps. It can affect both males and females at all ages and in all ethnic groups.

There are five groups of photodermatoses: primary or autoimmune photodermatoses (the exact cause remains to be elucidated, although an auto-immunologic mechanism in which the body attacks on itself with sun exposure is most likely); photodermatoses induced by exogenous drugs/chemicals (many drugs can interact with sunlight and provoke skin diseases); photo-exacerbated dermatoses (skin diseases which can worse with sunlight); metabolic and genetic photodermatoses (diseases associated with deficiency of certain enzymes or DNA defects, respectively, that leads to photosensitivity).

The next table gives examples of the most frequent diseases in each group.

Group of photodermatosesExamples of diseases

Primary or autoimmune

Polymorphic light eruption

Juvenile spring eruption

Actinic prurigo

Solar Urticaria

Chronic actinic dermatitis

Induced by exogenous drugs /chemicals

Drugs like thiazides, tetracyclines, non-steroidal anti-inflammatory drugs, phenothiazines, quinine, vemurafenib, among others; psoralens in plants, vegetables, fruit; fragrances in cosmetics; sunscreen chemicals; dyes and disinfectants

Photo-exacerbated dermatoses

Cutaneous lupus erythematosus

Dermatomyositis

Rosacea

Melasma

Metabolic

Porphyria cutanea tarda

Genetic

Xeroderma pigmentosum

3 - SYMPTOMS

Photodermatoses usually affect the areas exposed to sunlight, usually the face, neck and hands and do not affect areas not exposed to the light (covered at least by underwear), or are less severe in covered areas. The lesions can be of different forms: redness with or without scaling, vesicles and blisters, and be similar to an eczema or sunburn. Itching is frequent.

4 - CAUSES

The exact mechanism that is at the base of photosensitization is not yet fully clarified, but it is known that alterations on DNA and immunologic phenomena induced by radiation contribute specifically to the pathogenesis of some diseases such as lupus erythematosus. Some exogenous drug and chemicals can induce photosensitivity, already specified in the previous table.

5 - TREATMENT

Management of photosensitivity involves sun protection and treatment of the underlying disorder oriented by your doctor, who diagnoses the specific type of photosensitivity by taking a careful history, examining the skin and performing specific tests.

Mainly, photosensitivity reactions are prevented by careful protection from sun exposure and avoidance of exposure to artificial sources of UVR. Use of websites and smartphone apps that indicate local ultraviolet levels are helpful to understand when protection is most essential.

6 - TIPS FOR MANAGING

Management of photodermatoses involves sun protection and treatment of the underlying disorder, according to the specific cause, with systemic medication, topical medication, phototherapy, and others. For instance, cutaneous lupus erythematosus must be primarily controlled with appropriate systemic and/or topical drugs prescribed by your doctor. In photodermatoses induced by exogenous drugs, the suspected drug must be stopped or replaced immediately. For all groups of photodermatoses, sun protection is one of the essential parts of management and involves (according the grade of severity of the diseases).

 

  • Avoiding exposure to direct sunlight;
  • Staying indoors and away from windows, and seeking shade when outdoors;
  • Dressing up in covering clothing and wearing a wide-brimmed hat when outdoors. Some clothing is labeled with ultraviolet protection factor (UPF). Best protection from clothing is obtained from thick, dry and dark colored polyester, denim or wool;
  • 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;
  • Choose gray-tinted laminated glass for automobile;
  • Apply photoprotective UV films to windows at home, school work, and vehicles;
  • Take vitamin D supplements;
  • Have regular skin checks to locate and treat skin cancers early.

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