Photosensitivity is an abnormal reaction of the skin to sunlight, especially to the sun’s ultraviolet (UV) rays. It results in skin rashes that occur upon exposure to sunlight or other sources of ultraviolet radiation (UVR), such as fluorescent lamps, tanning beds and sun lamps.

Skin normally reacts to sun exposure by tanning or burning after a certain period of time. Photosensitive reactions may appear as intense sunburns or hives. Depending on the severity of the condition, it may occur quickly or develop a few hours after sun exposure.

Photosensitivity may be caused by an allergic reaction to sun exposure that triggers an immune system response in certain sensitive individuals. The reason for this type of immune system reaction is not known. These so-called sun allergies include polymorphous light eruption and solar urticaria.

Risk factors for developing photosensitivity may include chronic skin conditions (e.g., rosacea) and use of certain medications (e.g., antibiotics).

In rare cases, photosensitivity is the result of a defect in the body’s ability to repair skin cells that have been damaged by ultraviolet radiation. This only occurs in certain genetic diseases, such as xeroderma pigmentosum and Cockayne syndrome.

To diagnose photosensitivity, a physician may take a patient’s complete medical history and perform blood and allergy tests to identify allergens (substances the body mistakenly perceives to be a threat, triggering an allergic reaction).

Photosensitive reactions (e.g., papules, hives) may be treated like other skin rashes or sunburns with cool oatmeal baths or other measures. Physicians may also recommend medications such as antihistamines or corticosteroids to relieve symptoms.

For people with photosensitivity, avoidance is the best prevention method. Staying out of sunlight as much as possible can effectively reduce photosensitive reactions. When venturing out into sunlight, it is essential to wear a hat and clothing that covers as much skin as possible. Hypoallergenic sunscreen (made with ingredients that do not trigger allergic reactions) can be used to protect exposed skin.

Photosensitivity is the medical term used to describe an abnormal reaction of the skin to sunlight, especially to the sun’s ultraviolet (UV) rays. Photosensitive individuals often develop a skin rash triggered by exposure to ultraviolet radiation (UVR).

All skin is photosensitive to some degree. That is, it undergoes changes when exposed to UV light to protect against damage. When skin is exposed to sunlight or other sources of UVR (e.g., sun lamps, fluorescent lamps, tanning beds), the outer protective layer of skin (epidermis) darkens to block UV light from penetrating deeper into the tissue. This occurs because the pigment-producing skin cells (melanocytes) make increased amounts of melanin, the pigment that gives skin its color. The new melanin eventually travels to the surface of the skin, and the skin becomes darker in appearance (tans).

Individuals with photosensitivity often develop a skin rash triggered by exposure to ultraviolet radiation (UVR). This may occur as a result of the following conditions:

• Immune system reaction. For unknown reasons, certain individuals’ immune systems recognize sun-altered skin as a threat to the body and respond by triggering a skin reaction. This is also called a sun allergy. Sun allergies include:
  
  
• • Polymorphous light eruption (PMLE). Multiple red papules or patches on sun-exposed skin (e.g., neck, chest, arms, lower legs) that appear within the first two hours of sun exposure. Other symptoms include itchiness (pruritus), chills, headache, nausea and malaise (general ill feeling). PMLE is more common in women than men.
    
    
  • Solar urticaria. Itchy hives that appear on skin within minutes of sun exposure. The hives may vary in size from as small as a pencil eraser to as large as a dinner plate and may overlap to create large areas of swelling. People with large affected areas often experience headaches, weakness and nausea. Though hives will often disappear without treatment, they usually return with further sun exposure. Solar urticaria most often affects young women.
    
    
• A defect in skin cell repair (rare). Exposure to UVR damages the DNA (the genetic material within a cell) in skin cells and disrupts normal cell functioning. Generally, in healthy people damaged DNA is repaired by the DNA repair system. Patients with rare genetic diseases including xeroderma pigmentosum (a rare degenerative disease involving sensitivity to light that develops in the first few years of life) and Cockayne syndrome (genetic condition characterized by short stature, premature aging, sensitivity to light and possible deafness and mental retardation) often experience severe, life-threatening photosensitivity due to a defect in their body’s ability to repair DNA damaged by UVR.

The use of certain medications and substances may increase the skin’s sensitivity to sunlight or other sources of UVR in some people. In such cases, hyperpigmentation (a condition in which patches of skin become darker than surrounding skin) may accompany the photosensitive rash. Medications that may cause photosensitivity include:

• Antibiotics
  
  
• Birth control pills
  
  
• Nonsteroidal anti-inflammatory drugs ([NSAIDs], which include ibuprofen and naproxen)
  
  
• Diuretics
  
  
• Coal tar (topical medication used to treat skin disorders)
  
  
• Antiarrhythmics (medications used to treat abnormal heart rhythms)
  
  
• Antidepressants
  
  
• Oral antidiabetics (medications used to treat diabetes)

Substances applied directly to the skin (e.g., lotions, creams, perfumes) that may induce photosensitivity include:

• Sunscreens that contain para-aminobenzoic acid (PABA), cinnamates, benzophenones or salicylates
  
  
• Fragrances such as musk ambrette and 6-methylcoumarin

Photosensitivity may also occur following exposure to certain plants. Plants that may trigger photosensitivity after being touched include:

• Celery
• Parsley
• Parsnips (leaves)
• Carrots (leaves)
• Figs
• Citrus fruit
• Hogweed

In addition, individuals with certain skin conditions may be prone to developing photosensitivity. Skin conditions that may be aggravated by UVR exposure include:

• Acne. An inflammatory skin disorder characterized by outbreaks of whiteheads, blackheads and pimples.
  
  
• Atopic dermatitis. An inflammation of the skin caused by allergies.
  
  
• Seborrheic dermatitis. An inflammation of the upper layers of the skin that causes a scaly, itchy rash with or without reddened skin.
  
  
• Rosacea. A condition that leads to redness, inflammation and acne-like lesions on the nose, forehead, cheeks, chin and sometimes the eyes.
  
  
• Psoriasis. A common disorder that can affect any part of the body. It is characterized by raised, inflamed lesions that join together to form plaques (patches) with distinct borders that are covered with flaky scales.
  
  
• Bullous pemphigoid. Chronic blistering of the skin that ranges from mildly itchy welts to severe blisters and infection.
  
  
• Lupus. An autoimmune disease that affects various organs in the body including the skin.
  
  
• Lichen planus. A skin condition characterized by angular, purple papules that are inflammatory and pruritic (itchy).
  
  
• Herpes. A sexually-transmitted disease characterized by the appearance of blisters or sores on the mouth, lips, gums and genitals.
  
  
• Porphyria. A group of diseases characterized by increased amounts of porphyrins (a naturally occurring chemical) in the skin.

The most common symptom of acute photosensitivity is lesions or blisters on the skin following sun exposure or exposure to other sources of ultraviolet radiation (UVR), such as sun lamps, fluorescent lamps and tanning beds. The specific appearance of the skin and any other symptoms may differ depending on the severity of photosensitivity.

Other symptoms may include:

• Hives
  
  
• Itchiness (pruritus) on the affected areas
  
  
• Inflammation
  
  
• Edema (swelling)
  
  
• Hyperpigmentation (condition in which patches of skin become darker in color than surrounding skin)
  
  
• Headache
  
  
• Chills
  
  
• Nausea
  
  
• Malaise (general ill feeling)

Individuals experiencing these symptoms after exposure to the sun or other sources of UVR should contact their physician immediately.

The diagnosis of photosensitivity typically begins with a physician consultation (usually with a dermatologist). The physician may compile a detailed medical history and ask questions about any family history of allergies or diseases. The physician may also inquire about exposure to possible irritants, current medications, over-the-counter drugs or herbal products. It is important to discuss the use of all current medications or herbal remedies even if they are not used daily.

During a subsequent physical examination, the physician will meticulously examine the skin and ask questions about when the skin reaction occurs in relation to sun exposure or other sources of ultraviolet radiation.

The physician may perform tests including:

• Allergy tests. Help identify specific allergens (substances the body mistakenly perceives to be a threat, triggering an allergic reaction). Tests include skin tests in which the skin is pricked or injected with an allergen. If a red and swollen area of the skin (e.g., rash, hive) appears at the test site, the test is positive for that allergen. Blood tests (e.g., RAST test) may also be used to measure the levels of immunoglobulin E (a protein involved in allergic reactions) in response to the introduction of a specific allergen.
  
  
• Blood tests. Tests that identify abnormally high or low levels of a given substance in the blood. Blood tests can identify underlying diseases or conditions that may be causing the skin reaction.
  
  
• Skin biopsy. Laboratory test that examines a small piece of skin that has been removed by the physician.
  
  
• Photo-testing. Test that exposes a small area of skin to measured amounts of ultraviolet light. If skin symptoms appear, the test will confirm that they are related to sun exposure. Symptoms usually appear within 30 minutes of exposure.

Generally, people with polymorphous light eruption (PMLE) who continue to go out in the sun gradually become less sensitive to the effects of sunlight. Photosensitive reactions (e.g., papules, hives) may be treated like other skin rashes or sunburns. Patients may find that cool oatmeal baths are helpful in relieving the intense itching (pruritus) associated with photosensitive skin reactions. Medications may be recommended or prescribed to treat moderate hives. The standard medications are antihistamines, which are available in both prescription and non-prescription forms. For more severe cases, corticosteroids may be recommended for the rapid reduction of swelling and itching.

In extreme cases of solar urticaria, antimalarial drugs may be prescribed for their anti-inflammatory properties.

For reactions caused by medications, patients can avoid sun exposure while taking the medication. This can be achieved by wearing clothing that covers most of the skin and using hypoallergenic sunscreen (made with ingredients that do not trigger allergic reactions). If other types of medications are available, discussion with a physician may identify alternative treatments that may not cause a reaction. Medication options should always be discussed with a physician.

Some chronic illnesses or disorders may need long-term treatment options for photosensitivity. Desensitization to sunlight or heat for PMLE and solar urticaria are possible treatments for severe cases. Desensitization involves limited and controlled exposure to the allergen in a medical setting. A short dose of ultraviolet light is used to desensitize patients with PMLE and solar urticaria. A six-week course of desensitization often provides a PMLE patient with protection for the entire summer.

Avoidance is the best prevention method for skin rashes due to photosensitivity. For people who are photosensitive, sun protection is necessary regardless of weather conditions, and even in the shade. Covering the skin with clothing while exposed to sunlight will help to avoid the development of rashes or hives. Sunscreen or sunblock with a sun protection factor (SPF) of 30 or higher should be applied thoroughly on all areas of the skin that could be exposed to the sun (unless the sunscreen is an allergen capable of causing a photoallergic eruption). Sunscreens should be used in conjunction with the avoidance of sunlight and not as a substitute for it.

People with photosensitive conditions should also avoid other sources of UV light, such as sun lamps or tanning beds. People who are affected by fluorescent lamps can replace these light sources with tungsten light bulbs. Since UVR can pass through glass, patients may also benefit from applying a UVR-absorbing film on the windows in their home and car.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctors the following photosensitivity-related questions:

1. Am I at risk for developing photosensitivity?
   
   
2. Do my symptoms indicate photosensitivity?
   
   
3. What tests will you use to determine if I have photosensitivity?
   
   
4. What may have caused me to develop photosensitivity?
   
   
5. Does photosensitivity pose a danger to my overall health?
   
   
6. What are my treatment options? How effective are they?
   
   
7. Do I need to make any lifestyle changes to treat my photosensitivity?
   
   
8. What steps can I take to prevent photosensitivity-related skin rashes?
   
   
9. When can I expect my symptoms to subside?
   
   
10. Are my children likely to develop photosensitivity as well?