Know About Polymorphous light eruption
Polymorphous light eruption or PLE is the commonest form of photosensitivity disease after exposure to sun. The exact mechanism of development of PLE is not clearly known. Most of the individuals who suffer from PLE never seek medical attention due to the fact that PLE is often transient, which generally manifest at the initial exposure to sun during spring and then subsides spontaneously if the individual continue exposure to sun, which is known as “hardening” in common language. Most of the individual think and accept “hardening” as a natural phenomena after exposure to sun and accept it as natural and do not seek medical attention.
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The Photosensitivity Diseases
It is important to about the photosensitivity diseases (what are the photosensitivity diseases, how they are caused etc.). It is important to know what are the photosensitivity diseases. The photosensitivity diseases can be classified as genetic, metabolic, phototoxic, photoallergic, neoplastic & degenerative, idiopathic (cause unknown) and diseases aggravated by exposure to sun (photoaggravated) etc.
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What is Photosensitivity Disease?
Diagnosis of photosensitivity disease may be very difficult and need careful history about the duration of exposure to sun as well as duration of the signs and symptoms, the length of time between exposure to sunlight and the development of signs & symptoms (subjective complaints), and visible changes in the skin. Some times age of onset can be very helpful in diagnosing a photosensitivity disease; e.g. acute photosensitivity of erythropoietic protoporphyria generally (almost always) begins during childhood, whereas the chronic photosensitivity of porphyria cutanea tarda (PCT) usually begins in the fourth and fifth decades of life.
A history of exposure to drugs (both topical and systemic) and chemicals can provide important clue in diagnosing a photosensitivity disease. Many groups of drugs can cause photosensitivity by phototoxicity or by photoallergy. There are many chemicals which can cause photosensitization like fragrances like musk ambrette (were previously used in numerous cosmetic products).
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Skin Cancers due to Sun Exposure
Exposure to sun causes nonmelanoma cancers and melanoma of the skin. But the evidence of the role of sun exposure in causation of nonmelanoma (basal cell carcinoma and squamous cell carcinoma) is more direct than in melanoma. As approximately 80% of nonmelanoma skin cancers develop on exposed parts of body, including the face, the neck, and the hands. So for maintaining patients’ health state of skin health it is better to avoid sun as much as possible.
Risk factors of skin cancer:
Major risk factors of skin cancer are male sex, childhood sun exposures, older age, fair skin (white race), and residence at latitudes closer to the equator. Whites of darker complexions (like Hispanics) have one-tenth the risk of developing skin cancers compared to fair-skinned individuals. Blacks are at substantially reduced risk for all forms of skin cancer.
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How Skin Cancer Develop due to Sun
Chronic exposure to sunlight can cause malignant and non malignant effects (sunburn and vitamin D synthesis) and affects patients’ health state. The major known effect of chronic skin exposure to sunlight is nonmelanoma skin cancer. There are two types of nonmelanoma skin cancer and they are basal cell carcinoma (BCC) and squamous cell carcinoma (SCC).
Steps of skin cancer development:
There are three major steps for cancer induction and they are initiation of cancer, promotion of cancer, and progression of cancer. Chronic exposure of human skin to sun results in initiation (of cancer).
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Effects of Solar Radiation on Human Skin
Sunlight is the most visible and most obvious source of comfort in the environment. The sun provides the beneficial effects like warmth and vitamin D synthesis. But, acute and chronic exposure to sun may also have serious pathologic consequences, like exposure to sunlight is the major cause of human skin cancer and it also can exert immunosuppressive effects as well.
The energy of sun reaching the surface of the earth is limited to components of the ultraviolet (UV), the visible light, and the infrared portion of wavelength. At the short end of the UV is at approximately 290 nm (nanometer) as the cutoff (this is primarily due to stratospheric ozone formed by highly energetic ionizing radiation, which prevents penetration of shorter, more energetic, potentially more harmful wavelengths of solar radiation to the surface of the earth). Due to the concern about destruction of the ozone layer mainly by chlorofluorocarbons released into the atmosphere has led to international agreements to reduce production of chlorofluorocarbons and other ozone layer destroying chemicals.
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Photoprotection: The Need
Photosensitivity of the skin results from exposure to sunlight, so absolute avoidance of the sun would eliminate these disorders. Unfortunately, modern contemporary life-styles make this an impractical alternative for most individuals, and this has led to a search for better approaches to photoprotection.
The structural proteins in the epidermis (the outer layer of the skin) confer natural photoprotection, in particular keratins and melanin (pigment responsible for color of the skin). The amount of melanin and its distribution in cells is genetically regulated, and individuals of darker complexion (skin types IV–VI) are at decreased risk for the development of acute sunburn and cutaneous malignancy and other photosensitivity diseases.
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Phototoxic & Photo-allergic Drugs
There are many drugs which can cause photoallergy and phototoxicity. The commonly used drugs which can cause phototoxicity and photoallergy are given below:
Some examples of phototoxic drugs are given here:
-5- Fluorouracil
-amiodarone
-dacarbazine
-fluoroquinolones (ciprofloxacin, ofloxacin etc.)
-furosemide
-nalidixic acid
-phenothiazines
-psoralens
-retinoids
-sulfonamides
-sulfonylureas (e.g. glimeperide used in treatment of diabetes)
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Phototoxicity & Photoallergy
These photosensitivity (phototoxicity and photoallergy) disorders are related to the topical and/or systemic administration of drugs and as well as other chemicals. Both reactions (phototoxicity and photoallergy) require the absorption of energy by a drug or chemical resulting in the production of an excited-state photosensitizer that can transfer its absorbed energy to a bystander molecule or to molecular oxygen, thereby generating tissue-destructive chemical species.
Phototoxicity is a nonimmunologic reaction caused by drugs and chemicals. The clinical manifestations of phototoxicity include erythema (redness of skin) resembling a sunburn reaction that quickly "peels," within several days. In addition there may also be edema, vesicles, and bullae.
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Vitamin D Synthesis: Acute Effect of Sun Exposure
The effects of acute exposure to sun are sunburn and synthesis of vitamin D. vitamin D is one of the vitamin (other vitamin which is synthesized in the body is vitamin K in the gut, by gut flora but not adequate for human requirement) which human body can synthesize in the body in adequate amount and vitamin D is required by human body for good health state. Vitamin-health is an important aspect for good health state and vitamin D is vital for this.
How vitamin D is synthesized in the skin?
Upon exposure of skin to sunlight (UV-B or ultraviolet B, which consists of wavelengths between 290 and 320 nm), there occurs photolysis of epidermal 7-dehydrocholesterol converting it to pre-vitamin D3. This pre-vitamin D3 than then undergoes isomerization which is temperature-dependent to form the stable hormone vitamin D3.
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