Diseases

Photodynamic therapy utilizes the concept of sun or light sensitivity to treat some skin conditions including skin pre-cancers (actinic keratosis), skin cancers, and acne. Briefly, this treatment takes advantage of activating a photosensitizing drug (such as 5-aminolevulinic acid) by shining light directly onto it for a short time. The drug is first applied to the area of the skin where the cancer or pre-cancer is found. With light-induced activation of the drug, the abnormal cells (cancer or pre-cancer) are destroyed preferentially.

Some medical conditions are known to cause sensitivity to sun exposure. Systemic lupus erythematosus (SLE) often causes a rash on the face which can be very sensitive to sunlight. This rash is typically seen on the nose and cheeks, called a malar rash, and is considered one of the hallmarks of lupus. Porphyria is another medical condition that may cause photosensitivity reactions. This is a hereditary condition with skin manifestation (cutaneous porphyria) causing rashes and blisters in reaction to exposure to sunlight. Vitiligo is a relatively common disorder that causes patches of white de-pigmented skin. These patches lack melanin and are extremely sensitive to UV rays. Xeroderma pigmentosum is a disorder that appears to result from an inherited hypersensitivity to the cancer-causing (carcinogenic) effects of ultraviolet light. Sunlight causes DNA damage that is normally repaired. Individuals with xeroderma pigmentosum have defective inability to repair the DNA after UV damage. Affected individuals are hundreds of times more vulnerable to developing skin cancer than other people. Their extreme skin photosensitivity predisposes them to pronounced skin damage and scarring and also to the early onset of skin cancer (basal cell and squamous cell carcinomas and malignant melanoma). Individuals with classic oculocutaneous albinism lack melanin in their skin and eyes -- hence, the term "oculocutaneous" ("oculo" for eyes, and "cutaneous" for skin). Without the protection of this pigment, their white skin and pink eyes are both highly sensitive to UV and susceptible to the rays' damage.

Some vegetables and plants may cause sun sensitivity if they come into contact with the skin. Mango peel, lime juice, parsnips, or celery, for example, may cause temporary discoloration (darkening) of the skin contact area when in the sun. Common phototoxic fruits and vegetables include:

• Lime
• Celery
• Carrots
• Figs
• Parsley
• Parsnips
• Mango peel

The diagnosis is mainly made by a thorough history, examination, and review of the medications and duration of exposure to sun. It is important to ask when the medication was started and for how long the symptoms persisted. There are no diagnostic tests available, although a photo-patch test may be performed. This test is typically performed by a dermatologist (a doctor who specializes in diseases of the skin) by shining light onto different areas of the skin to see how long it will take for the light to cause redness. This test may be useful in evaluating photosensitivity to topical medications causing a photoallergic response. In cases of phototoxicity reactions, this test is generally not useful.

Not everyone taking any of these drugs will develop photosensitivity reactions. Certain individuals have more susceptibility to these medications than others.

Symptoms of phototoxic reaction Individuals with phototoxic reactions may initially complain of a burning and stinging sensation. Then the redness typically occurs within 24 hours of the exposure to sun in the exposed areas of the body such as the forehead, nose, hands, arms, and lips. In severe cases, the sun protected areas of skin may be also be involved. The range of skin damage may vary from mild redness to swelling to blister formation (bullae) in more severe cases. The rash from this photosensitivity reaction usually resolves with peeling and sloughing off (desquamation) of the affected skin within several days. Symptoms of photoallergic reactions Individuals with photoallergic reactions may initially complain of itching (pruritus). This is then followed by redness and possibly swelling and eruption of the involved area. Because this is considered an allergic reaction, there may be no symptoms for many days when the drug is taken for the first time. Subsequent exposure to the drug and the sun may cause a more rapid response in 1-2 days. Hyperpigmentation after reaction Hyperpigmentation (darkening) of the affected area of the skin may develop after the resolution of a phototoxicity reaction, but it is rare in a photoallergic reaction. In phototoxic reactions, high doses of the drug and long exposures to light may be required to cause the reaction.

Photosensitivity (or sun sensitivity) is inflammation of the skin induced by the combination of sunlight and certain medications or substances. This causes redness (erythema) of the skin and may look similar to sunburn. Both the photosensitizing medication or chemical and light source have to be present in order for a photosensitivity reaction to occur. Generally, these reactions can be divided into two mechanisms, 1) phototoxic reactions, and 2) photoallergic reactions. Phototoxic drugs are much more common than photoallergic drugs.

Phototoxic reactions In phototoxic reactions, the drug may become activated by exposure to sunlight and cause damage to the skin. The skin's appearance resembles sunburn, and the process is generally acute (has a fast onset). Ultraviolet A (UVA) radiation is most commonly associated with phototoxicity, but ultraviolet B (UVB) and visible light may also contribute to this reaction. Rash from a phototoxic reaction is mainly confined to the sun-exposed area of the skin. A phototoxic reaction typically clears up once the drug is discontinued and has been cleared from the body, even after re-exposure to light. Photoallergic reactions In photoallergic reactions, the ultraviolet exposure changes the structure of the drug so that is seen by the body's immune system as an invader (antigen). The immune system initiates an allergic response and cause inflammation of the skin in the sun-exposed areas. These usually resemble eczema and are generally chronic (long-lasting). Many drugs in this family are topical drugs. This type of photosensitivity may recur after sun exposure even after the drug has cleared from the system and can sometimes spread to areas of the skin unexposed to the sun.

Recognizing and discontinuing the photosensitizing drug is the most important step in treatment. In general, the usual sunburn prevention methods such as the use of sunscreens and avoidance of prolonged exposure to sun are important steps to take. Keeping the area of skin eruption moist and applying wet dressings may help relieve the symptoms. The reaction may last up to a few weeks. Topical steroid creams may be helpful in treating the redness, and antihistamines are generally helpful in minimizing the itching. In severe cases, a short course (10-14 days) of oral steroids, under the direction of a doctor, may be used.

Ultraviolet (UV) light is radiation energy in the form of invisible light waves. UV light is emitted by the sun and by tanning lamps. The sun discharges three types of ultraviolet radiation:

1. ultraviolet A (UVA)
2. ultraviolet B (UVB)
3. ultraviolet C (UVC)

Only UVA and UVB rays reach earth. (UVC does not penetrate the earth's upper atmosphere.) Tanning lamps also produce UVA and/or UVB. These artificial rays affect the skin in the same way as do UVA and UVB from the sun.