Photosensitivity Skin Disorders
These are conditions where the skin reacts abnormally to light, especially ultraviolet light. Photosensitivity skin disorders (PSD) are classified by the wavelength to which the individual reacts.
Some PSD are due to the presence of drugs,
hormones or heavy metals in the individual's skin. Photoallergies may also
result when light rays interact with certain chemicals. Photocontact
allergens include:
- phenothiazine (a type of tranquilizer)
- sulfonamides (a type of antibiotic)
- hexachlorophene
- sunscreen agents
- optical bleaches
- topical antihistamines
Polymorphous Light Eruption
295-365 nanometer wavelengths
This is a common skin eruption of unknown cause and is commonly known as "sun poisoning". It occurs in susceptible individuals when they are exposed to solar radiation that is more intense than usual, i.e. as in the first time in the sun that season or a body part that has no prior UV exposure. It may also occur when the patient travels to a higher latitude or lower latitude. The skin-rash reaction heals within 7-10 days if additional sun exposure is avoided. Sunscreens are mandatory to protect from UVA and UVB, although UVA protective agents are more effective in preventing these eruptions.
Polymorphous light eruption affects 10-14% of the white population. Most susceptible individuals are female. Onset of polymorphous light eruption usually occurs in the first 30 yrs of life.
Porphyrias
400-414 nanometer wavelengths
Porphyrias are caused by an inherited or acquired abnormality in heme (blood) metabolism. This abnormality causes the body to form and excrete excessive amounts of heme metabolites. The actual photosensitivity begins in childhood on sun-exposed areas.
Individuals who suffer from porphyria must be protected from solar radiation
by a physical blocking agent or by clothing. Some porphyria sufferers respond
to oral beta carotene.
Solar Urticaria
290-515 nanometer wavelengths
Solar urticaria is a rare reaction to sun or UV exposure. This is a true photoallergy. It develops rapidly--moments after exposure, the skin begins to itch, and then becomes red. Wheals or vesicles appear. The actual mechanism that causes this reaction is unknown, however, antihistamines are effective in treating the reactions of some patients.
Chronic Actinic Dermatitis
290 nanometer wavelengths to visible light
This disease has been previously described as chronic photosensitivity dermatosis. It appears initially as red spots and patches in sun-exposed areas of the scalp, rim of the ears, back of the neck, forearms, and back of the hands. Usually this looks like contact dermatitis. However, the condition can progress to a pattern that looks like cutaneous T-cell lymphoma. At this stage, there is a gradual spreading of red patches, interspersed with spider-weblike blood vessels that are visible through the skin.
The portion of the light spectrum causing this condition varies from person to person. It is important to do phototesting to find out which wavelengths are most dangerous to each individual. Such individuals must thereafter avoid sunlight, and must use sunscreens to prevent their reactions when they cannot avoid the sun. Chemical treatment options include oral azathioprine, PUVA, prednisone, etretinate, and cyclosporin.
Persistent Light Reaction
290-400 nanometer wavelengths
This is a continued overreaction of the skin to sun exposure even when subsequent exposure is avoided. Persistent light reaction causes photosensitive dermatitis. The condition usually resolves by itself within months of exposure. However, it may persist indefinitely. In some patients the reaction is severe enough that the skin becomes scaly and falls off. This is called generalized exfoliative dermatitis.
Sometimes the mechanism of this reaction is an ongoing exposure to a chemical that is not correctly identified and removed from the body or environment. In other cases the reactive chemical may be bonded to dermal proteins and so cannot be removed. Sometimes the cause of this skin reaction cannot be identified.
Lupus Erythematosus (LE)
290-330 nanometer wavelengths
LE has two manifestations: cutaneous and noncutaneous. Noncutaneous LE is a chronic inflammatory disease of connective tissue. This autoimmune condition is sometimes exacerbated after exposure to sunlight.
Cutaneous lupus erythematosus (LE) is a chronic disease of unknown origin.
It occurs in two general forms:
- discoid form
- subacute form
The discoid form causes well-defined lesions. These scaly patches are found on the head and neck. When the lesions heal, they leave atrophied (shrunken) tissue, scarring, and pigmentation changes.
The subacute form causes papulosquamous or polycyclic lesions around the neck, the outer aspects of the arms, and the trunk. Papulosquamous lesions are red elevated areas. Polycyclic lesions show up as patches of many, rounded lesions. The lesions caused by the subacute form of lupus erythematosus are milder than in the discoid form. The lesions of the subacute form also heal without scaring or atrophy.
UVB appears to be more important than UVA in causing the lesions in LE. However, in some individuals, UVA plays a greater role. People who suffer from LE should use a broad-spectrum sunblock and avoid exposure to the sun. Oral antimalarials have been successfully used to treat some LE sufferers.
Xeroderma pigmentosum
290-340 nanometer wavelengths
Xeroderma pigmentosum is an autosomal, recessive disorder. It results from a
genetic defect in the body's ability to repair its own DNA. Individuals with
this rare disease suffer from skin discoloration, ulcers, skin and muscle
atrophy. These people are subject to premature development of skin cancers.
Xeroderma pigmentosum sufferers must be careful to protect their eyes and skin
against the sun. They should also watch for early signs of skin cancer.
Albinism
Albinism is a nonpathological defect in the formation of pigmented vesicles (melanosomes). Although albinos have pigment cells (melanocytes) in their skin, hair, and eyes, those tissues lack pigment itself.
Especially in sunny climes, albinism sufferers should be careful to use
sunscreens and avoid sun exposure. Albinism patients in sunny climes who are
not careful to avoid sun exposure often develop malignant or premalignant skin
lesions by early adulthood. Oddly enough however, melanoma is rare in albinos.
|
Search our Site!
Type Key word
|
|
|
|
|
|
|
|
|
|
|
|
|