Abnormal responses to sunlight or artificial light due to extreme reactivity of light-absorbing molecules in tissues. It refers almost exclusively to skin photosensitivity, including sunburn, reactions due to repeated prolonged exposure in the absence of photosensitizing factors, and reactions requiring photosensitizing factors such as photosensitizing agents and certain diseases. With restricted reference to skin tissue, it does not include photosensitivity of the eye to light, as in photophobia or photosensitive epilepsy.

Photosensitivity refers to various symptoms, diseases, and conditions (photodermatoses) caused or exacerbated by exposure to sunlight. It is classified into five categories: primary photodermatosis, exogenous photodermatosis, photo-exacerbated dermatoses, metabolic photodermatosis, and genetic photodermatosis.

Primary or autoimmune photodermatoses

• Polymorphic light eruption

• Juvenile spring eruption

• Actinic folliculitis

• Actinic prurigo

• Solar urticaria

• Chronic actinic/photosensitivity dermatitis

• Hydroa vacciniforme (associated with Epstein-Barr virus)

Exogenous or drug/chemical-induced photodermatoses

• Drug-induced photosensitivity: common photosensitizing drugs are thiazides, tetracyclines, non-steroidal anti-inflammatory drugs (NSAIDs), phenothiazines, voriconazole, quinine, vemurafenib, and many others

• Photocontact dermatitis: due to phototoxic chemicals such as psoralens in plants, vegetables, fruit; fragrances in cosmetics; sunscreen chemicals; dyes and disinfectants

• Pseudoporphyria: induced by drugs and/or renal insufficiency

Photo-exacerbated or photo-aggravated dermatoses

Usually:

• Cutaneous lupus erythematosus (acute, subacute and chronic variants)

• Dermatomyositis

• Sjogren syndrome

• Darier disease

• Rosacea

• Melasma

Sometimes:

• Pemphigus vulgaris

• Pemphigus foliaceus

• Atopic dermatitis

• Seborrhoeic dermatitis

• Psoriasis

• Lichen planus (actinicus)

• Erythema multiforme

• Mycosis fungoides

Metabolic photodermatoses (rare)

• Porphyria cutanea tarda

• Erythropoietic protoporphyria

• Variegate porphyria

• Erythropoietic porphyria (Gunther disease)

Genetic photodermatoses (very rare disorders due to genomic instability)

• Xeroderma pigmentosum

• Cockayne syndrome

• Trichothiodystrophy

• Bloom syndrome

• Rothmund Thomson syndrome

Etiology

The etiology of a photodermatosis depends on its classification (see individual topic articles). Some are due to autoimmune reactions, drugs, connective tissue disease, and abnormal inherited biochemical pathways.

Epidemiology

Photosensitivity may be observed in both males and females at all ages and in all ethnic groups. Different types of photosensitivity may be prevalent at different times of life. Genetic and environmental factors intervene in the occurrence of photosensitivity.

Pathophysiology

Photosensitivity is caused by an abnormal reaction to a component of the electromagnetic spectrum of sunlight and a chromophore (reactive compound) within the skin. Patients can be sensitive to one kind of sunlight, for example only to ultraviolet radiation, ultraviolet A or B (UVA, UVB), or visible light, or to a wider range of radiation. The most common photosensitivity is to UVA. Mainly, exposure to visible light triggers porphyria.

Histopathology

Each category and sub-category of photosensitivity has a unique reaction pattern seen on pathology. See the individual chapter for the unique histopathologic characteristics of each entity.

History and Physical

The clinical features depend on the specific photodermatosis.

• Photodermatoses affect areas exposed to sunlight, usually the face, neck, hands, and do not affect areas not exposed to the light (covered at least by underwear), or are less severe in covered areas.

• Sometimes they spare areas that habitually are exposed to the light, for example, the face of a polymorphic light eruption.

• Sometimes they only affect certain parts of the body, for instance, juvenile spring eruption is confined to the tops of the ears.

• Photodermatoses may also occur following indoor exposure to artificial sources of UVR like fluorescent lamps or visible radiation.

• Genomic instability due to DNA repair deficiency disease causes pigmentary changes and high risk (1000 times normal) of skin tumors including basal cell carcinoma, squamous cell carcinoma, and melanoma.

• Children with the photosensitive genodermatoses have characteristic cutaneous features and abnormalities of other organs.

Clues to photosensitivity include:

• Summer exacerbation; although, note that many photodermatoses are present year round

• Sharp cut-off between affected area and skin covered by clothing or jewellery (e.g., watch strap, ring)

• Sparing of folds of upper eyelids

• Sparing of deep furrows on face and neck

• Sparing of skin covered by hair

• Sparing of skin shadowed by the ears, under the nose and the chin

• Sparing of the web spaces between the fingers.

Evaluation

Medical practitioners diagnose photosensitivity by a history of a skin problem arising from exposure to sunlight. They determine the specific type by taking a careful history, examining the skin and performing specific tests. Photosensitivity is sometimes confirmed by photosets, which only is available in specialized centers.

• Minimal erythema dose (MED) testing (broadband or monochromators) to determine threshold dose

• Provocation photoset procedure using repeated exposures to UVA and/or UVB over four consecutive days in an attempt to reproduce the dermatosis

• Photopatch tests in association with standard patch tests to determine photoallergy

Investigations may include:

• Full blood count

• Connective tissue antibodies including antinuclear antibodies (ANA), extractable nuclear antigens (ENA) if suspicious of lupus erythematosus

• Porphyrins in blood, urine, and feces

• Liver function and iron tests in patients suspected of porphyria

• Skin biopsy for histopathology and direct immune fluorescence in primary and photo-exacerbated dermatoses

• In cases suspicious of xeroderma pigmentosum, measurement of post-UV cell survival and DNA repair capacity in fibroblast assays

• Tiger hair appearance on polarised microscopy of brittle hair (dark and light areas) should lead to chromatography to determine amino acid content, which shows reduced cysteine in trichothiodystrophy

• Gene sequencing may confirm Bloom syndrome or Rothmund Thomson syndrome.

Treatment / Management

Management of photosensitivity involves sun protection and treatment of the underlying disorder. 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. There is more ultraviolet radiation in the tropics compared to temperate areas, in the Southern hemisphere compared to the Northern, during summer compared to winter, at high altitude compared to sea level, and in the middle of the day compared to the extremes of the day.

Protection involves:

• 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, tightly woven, 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

• Tanning products containing dihydroxyacetone provide modest photoprotection against UVA and to a lesser extent against UVB.

SPF is sun protection factor, defined as the dose of solar radiation needed to induce just perceptible erythema (minimal erythema dose, MED) on skin treated with 2 mg/cm sunscreen divided by the MED on untreated skin. SPF primarily describes protection from UVB, as it reflects protection from the erythema action spectrum.

The primary photodermatosis polymorphic light eruption may be paradoxically effectively treated by graduated, and cautious, exposure to ultraviolet radiation.

Differential Diagnosis

The first step in considering a diagnosis within the broad scope of photosensitivity is to consider each category of photosensitivity and the specific entities within the given category; whether it is primary photosensitivity such as polymourphous light eruption, autoimmune photosensitivity such as lupus erythematosus, photo-exacerbated or aggravated such as dermatomyositis, genetic such as xeroderma pigmentosum, or metabolic such as porphyria cutanea tarda. Then using the history and physical exam, narrow down the differential. For example, a polymourphous light eruption(PMLE) may be distinguised from lupus erythematosus by the history, presentation, and clinical appearance of these lesions. For photoexacerbated diseases such as dermatomyositis, other clinical findings such as capillary abnormalities around the nail folds or gottron papules over the bony prominences usually help with distinction from other entities such as drug enduced photosensitivity. Once the general category has been suspected, a differential can be developed within that category and helps with the diagnosis. For the differential diagnosis of each entity, please see the specific chapter of that entity.

Prognosis

The prognosis of each entity is unique, please see the individual chapters for each condition.

Complications

The complications of each entity is unique, please see the individual chapters for each condition.

Deterrence and Patient Education

In general, treatment of photosensitivity regardless of the entity is going to center around managing symptoms and pursuing photoprotection.

Pearls and Other Issues

Patients with photodermatoses also may need to:

• Take vitamin D supplements and oral antioxidants

• Wear a clear plastic mask to protect the face

• Choose gray-tinted laminated glass for automobile

• Apply photoprotective UV films to windows at home, school work, and vehicles

• Have regular skin checks to locate and treat skin cancers early.

Enhancing Healthcare Team Outcomes

The healthcare team, including nurses, pharmacists, and clinicians must work together to educate patients with photodermatoses as they need to be reminded to take vitamin D supplements and oral antioxidants, wear a clear plastic mask to protect the face, choose gray-tinted laminated glass for their automobile, and apply photoprotective UV films to windows at home, school work, and vehicles. The team should remind patients they need to have regular skin checks to locate and treat skin cancers early. [Level V]

When shopping for a sunscreen, consumers are faced with many choices. These choices include the sun protection factor (SPF) rating, which can vary from 8 to 50.

SPF is a measure of how much sunlight (UV radiation) is needed to develop sunburn after a sunscreen has been applied, compared to the amount of UV radiation required to develop sunburn on unprotected skin. The higher the SPF, the greater the protection is from UV radiation, and so the greater the sunburn protection.

It is important to know that SPF does not tell you how long you can be in the sun without getting sunburn. SPF does not mean that if you normally burn in 1 hour and you apply an SPF 8 sunscreen, it will take 8 hours for you to burn. Wrong. Instead, SPF tells you the amount of sunburn protection from UV radiation that is provided by sunscreens when they are used as directed – not burn protection time.

Several things can affect the amount of UV radiation exposure:

• time of day
• season
• geographic location
• altitude, and
• weather conditions (cloudy day versus clear)

For example, a person spending 15 minutes in the sun at noon in Boston without sunscreen may not sunburn, but that same person could burn after spending 15 minutes in the sun in Miami because of the higher amount of UV radiation exposure in the geographic location.

Skin complexion, amount of sunscreen applied, and how often you reapply can also affect exposure. In order for a sunscreen to be effective, it’s important that it be applied as directed, and reapplied as directed and needed based on physical activity. Participating in activities like swimming or activities that can promote heavy sweating may require more frequent reapplication.

Remember, SPF does not tell you how long you can be in the sun without getting sunburn. Instead, it’s a measure of the amount of sunburn protection from UV radiation that is provided by sunscreens when they are used as directed and as needed.

Fun in the sun can be had all year long -- hiking, winter skiing, swimming, or just enjoying the warmth of the sun. However, when taking certain medicines, life in the sun can sometimes be less than fun.

Some medicines contain ingredients that may cause photosensitivity -- a chemically induced change in the skin. Photosensitivity makes a person sensitive to sunlight and can cause sunburn-like symptoms, a rash or other unwanted side effects. It can be triggered by products applied to the skin or medicines taken by mouth or injected.

There are two types of photosensitivity – photoallergy and phototoxicity.

Photoallergy is an allergic reaction of the skin and may not occur until several days after sun exposure. Phototoxicity, which is more common, is an irritation of the skin and can occur within a few hours of sun exposure. Both types of photosensitivity occur after exposure to ultraviolet light – either natural sunlight or artificial light, such as a tanning booth.

There are certain types of medicines that can cause sensitivity to the sun. Some of these include:

• Antibiotics (ciprofloxacin, doxycycline, levofloxacin, ofloxacin, tetracycline, trimethoprim)
• Antifungals (flucytosine, griseofulvin, voricanozole)
• Antihistamines (cetirizine, diphenhydramine, loratadine, promethazine, cyproheptadine)
• Cholesterol lowering drugs (simvastatin, atorvastatin, lovastatin, pravastatin)
• Diuretics (thiazide diuretics: hydrochlorothiazide, chlorthalidone, chlorothiazide.; other diuretics: furosemide and triamterene)
• Non-steroidal anti-inflammatory drugs (ibuprofen, naproxen, celecoxib, piroxicam, ketoprofen)
• Oral contraceptives and estrogens
• Phenothiazines (tranquilizers, anti-emetics: examples, chlorpromazine, fluphenazine, promethazine, thioridazine, prochloroperazine)
• Psoralens (methoxsalen, trioxsalen)
• Retinoids (acitretin, isotretinoin)
• Sulfonamides (acetazolamide, sulfadiazine, sulfamethizole, sulfamethoxazole, sulfapyridine, sulfasalazine, sulfasoxazole)
• Sulfonylureas for type 2 diabetes (glipizide, glyburide)
• Alpha-hydroxy acids in cosmetics

Not all people who take or use the medicines mentioned will have a reaction. Also, if you experience a reaction on one occasion, it does not mean that you are guaranteed to have a reaction if you use the product again.

If you have concerns about developing a reaction, try to reduce your risk:

• When outside, seek shade, especially between 10 a.m. and 2 p.m. – some organizations recommend as late as 4:00 p.m. Keep in mind that the sun’s rays may be stronger when reflected off water, sand and snow.
• Wear long-sleeved shirts, pants, sunglasses, and broad-brimmed hats to limit sun exposure.
• Use a broad sunscreen regularly and as directed. Broad-spectrum sunscreens provide protection against ultraviolet A (UVA) and ultraviolet B (UVB) radiation. An SPF 15 is the minimum number needed to provide measurable protection; however, a sunscreen with an SPF value of 30 or higher is recommended. Rarely, some sunscreen ingredients can cause photosensitivity themselves.

If you have questions about your medications and the possibility of a photosensitivity, contact your health-care professional or pharmacists. Taking a few precautions can help limit your risk of photosensitivity and keep the sun shining on your fun.

Introduction

Polymorphic light eruption is the most common form of immunologically mediated photosensitivity dermatoses. Exposure to sunlight in spring or summer results in an irritable rash that resolves within a few days, providing further exposure is avoided. Variants include juvenile spring eruption (vesicles on the ears of young boys) and PMLE sine eruption (pruritus on sun-exposed skin without visible skin changes). Polymorphic light eruption is also known as polymorphous light eruption and prurigo aestivalis.

Etiology

The cause of polymorphic light eruption is unknown. It is postulated that there is a delayed hypersensitivity reaction to an endogenous antigen expressed after exposure to sunlight or artificial sources of ultraviolet (UV) radiation. Theories must account for increased prevalence in women and for the hardening effect of on-going exposure to ultraviolet radiation.

Epidemiology

The prevalence of polymorphic light eruption varies worldwide. Affected individuals may experience it every time they go outdoors, or only occasionally. It is more common in Northern Europe (15% in the UK) than in Australasia (5%). It affects all skin types but is more common in lighter skin especially Fitzpatrick skin phototype 1, than in darker skins. It most often (about 75% of cases) begins in females aged 20 to 40 years but may start in childhood or later in life. More people experience polymorphic light eruption at high altitude than at sea level.

Pathophysiology

Twin studies indicate a polygenic model may explain familial clustering. Sunburn reaction in patients affected by polymorphous light eruption is normal.

Current theories involve two steps that lead to a polymorphous light eruption. An unknown photoantigen is rendered immunogenic on exposure to UV. This does not cause a problem in unaffected individuals because of UV-induced suppression. In patients with a polymorphic light eruption, T–cell function is not suppressed by UV radiation until photo-hardening has taken place. The putative antigen induced by UV radiation leads to a predominance of CD4+ T cells and the production of proinflammatory cytokines such as interleukin (IL) 1. Vitamin D insufficiency, the role of estrogen in preventing UV-induced immune suppression, and dysregulated antimicrobial factors may be relevant.

The hardening effect, where further exposure to UV prevents the eruption, is not fully understood and could involve tanning, hyperkeratosis, and acanthosis of the epidermis, and/or the development of immunological tolerance.

Toxicokinetics

UV-A is the usual part of the electromagnetic spectrum that provokes polymorphous light eruption (75% to 90%). However, it can be triggered in some patients by UV-B or visible light. Exposure may be to sunlight or to an artificial or medical source of ultraviolet radiation.

History and Physical

The first sign of polymorphous light eruption typically appears after first exposure to intense sunlight during the spring or early summer in temperate climates. Several hours to days later, an irritable rash appears on areas newly exposed to the light such as the décolletage, forearms, backs of hands, lower legs and feet. It rarely affects the face. It also occurs in some patients treated for inflammatory skin diseases with phototherapy, when it may appear on the trunk and proximal limbs.

The most common morphology is smooth-topped erythematous papules, which can coalesce into plaques. Morphology varies between individuals and can include macules, vesicles, lichenoid plaques, prurigo papules and targetoid lesions resembling erythema multiforme.

Rarely, systemic features such as fever, malaise, and headaches, have been associated with the eruption.

The rash persists for several days then clears up without scarring if further exposure to UV is avoided. It may persist for weeks or months if repeatedly exposed, although in most individuals gradual exposure leads to hardening so that the eruption does not occur in late summer.

Polymorphic light eruption tends to recur annually and is some patients persists throughout the year, depending on latitude. It often reduces in severity over time and eventually resolves with a lower prevalence in older people.

Evaluation

Skin biopsy shows upper dermal edema, and a dense perivascular and periadnexal lymphocytic infiltrate without vasculitis. Plasmacytoid dendritic cells and T regulatory cells predominate. Neutrophils may be seen in early lesions. Spongiosis, vesicle formation, and liquefaction degeneration may be seen dependent on the clinical signs. Direct immunofluorescence testing is negative.

In most patients with a polymorphic light eruption, blood tests will reveal normal results. However, positive antinuclear antibody and extractable nuclear antigen (anti-Ro/La) in low titer may be detected, even in the absence of other criteria to suggest a diagnosis of lupus erythematosus. When the history or clinical findings indicate, urinary and red cell porphyrin screening may be performed and are negative.

Phototesting is rarely necessary. Specialized centers may undertake photoprovocation testing in late winter, to determine inciting wavelengths. This involves exposure of 5-cm squares of usually-affected skin to 1–2 minimal erythema doses (MED) of broadband UVB and to varying doses of UVA. The test is repeated on the same site daily for 3 days and the area examined to detect the typical rash. False negative responses occur in 10% to 40% of tested individuals. Formal monochromator MED testing is non-contributory, usually demonstrating expected results for the patient’s skin color.

Treatment / Management

Management requires determining what provokes the eruption and then attempting to minimize this, while at the same time gradually increasing exposure to induce hardening.

Explain that UV-A is a large component of sunlight and can cause the light eruption without sunburn (as sunburn is mainly due to UV-B). UV-A, unlike UV-B, can penetrate window glass and is less well blocked by sunscreens. When in situations that are likely to provoke the rash, cover up as much as possible with densely woven clothing. Select broad-spectrum, water-resistant semi-opaque sun protection factor (SPF) 50+ sunscreens and apply before exposure and every two hours on skin that is not covered.

Low-dose narrowband UV-B and other forms of phototherapy undertaken in late winter or early skin can reduce the incidence and severity of polymorphous light eruption. The course is 2 to 3 treatments per week for 4 to 6 weeks each year.

There is some evidence to support prophylactic short courses of oral steroids (for example, to prevent the eruption during a holiday break), hydroxychloroquine, and antioxidants such as Polypodium leucotomes extract, lycopene, beta-carotene, nicotinamide and astaxanthin.

The eruption is treated with topical corticosteroids with some benefit in reducing symptoms and duration.

Differential Diagnosis

The main differential diagnosis is photosensitivity associated with lupus erythematosus, which may behave and appear similar but tends to be more persistent. Solar urticaria occurs during or shortly after exposure and resolves within an hour or so of covering up. Photosensitivity dermatitis is more persistent with eczematous morphology.

Complications

Polymorphous light eruption is generally uncomplicated but severe disease can lead to emotional distress, anxiety and depression.

Enhancing Healthcare Team Outcomes

PLE is a relatively common skin disorder that is not easy to diagnose or manage. The disorder may be confused with many other skin disorders and thus is best managed by a dermatologist. However, once the diagnosis is made, the patient may be monitored by the primary care physician and nurse practitioner. These healthcare professionals should educate the patients on preventio which includes wearing appropriate garments when going outside and use ample sunscreen frequently.

The condition is benign but recurrences are common leading to emotional distress and isolation. Thus, a patient may benefit from a mental health counsultant.

Introduction

Solar urticaria is a chronic acquired photosensitivity disorder. It consists of recurrent episodes of urticaria rash developed on areas of the skin exposed to sunlight. Despite being usually a benign condition, it may be extremely disabling, thus limiting everyday activities and severely altering the quality of life of patients.

Etiology

Exposure of skin to sunlight causes solar urticaria. The radiation spectrum of action for solar urticaria ranges from ultraviolet B to visible light (wavelength of 300 nanometers to 500 nanometers) and is variable from one patient to another.

Epidemiology

Solar urticaria is an uncommon type of urticaria. It accounts for less than 0.5% of all urticaria cases and 7% of all photodermatoses. The disease usually begins in young adulthood (median age 35 years), but cases of onset in neonates or elderly persons have been reported. There is a female predominance but no ethnic difference. In the largest series of patients, a history of atopy is noticed in less than 30% of cases. The association of solar urticaria with other types of chronic urticaria may be seen in up to 16% of patients.

Pathophysiology

Solar urticaria pathophysiology is not entirely understood. It is an immediate hypersensitivity reaction, which might be IgE-mediated, occurring after exposure to the sun. The radiation may activate an endogenous substance called a chromophore, which could be present in the serum and/or the dermis, turning it into an immunologically active photo allergen. This later induces the degranulation of mast cells, resulting in lesions of urticaria. The intradermal positive reaction after injection of the patient’s irradiated serum is consistent with the hypothesis of a circulating chromophore.

Certain radiation wavelengths (usually long ones) may inhibit the immunological reaction induced by other wavelengths (usually short ones). This is called the double spectrum of action.

Occasionally, solar urticaria is triggered by an exogenous substance, such as some medications. Some examples include atorvastatin, chlorpromazine, tetracycline, or oral contraceptives.

Histopathology

The histopathology of solar urticaria almost mirrors other urticarias; the dermis shows mild edema with mixed infiltrate of neutrophils and eosinophils around the vasculature.

History and Physical

Erythema and edematous papules occur within a few minutes after exposure to sunlight, on sun-exposed areas, and even on areas covered with thin and white clothing that allows the solar radiation to reach the underlying skin. Usually, covered skin reacts more severely to the sun when it is exposed. The face and hand skin seem more tolerant to sun radiation. The rash is associated with a sensation of itching or burning. Periorbital and/or mucosal angioedema may also be observed. Dermographism may be noticed in some patients. Systemic symptoms such as nausea, wheezing, dyspnea, or syncope are not uncommon, especially if large areas of the skin are exposed to sunlight during a long period. However, even if systemic symptoms are present, anaphylactic shock rarely occurs in solar urticaria. The cutaneous symptoms resolve in 75% of cases within an hour following the interruption of sun exposure and more within 24 hours. The severity and the duration of the symptoms are also related to the intensity of light.

Evaluation

The diagnosis of solar urticaria is suspected on anamnesis (transient urticarial lesions occurring a few minutes after exposure to sunlight), while the physical examination is normal in the absence of sun exposure.

Symptoms and distribution of solar urticaria can mimic other acquired photodermatoses. Differential diagnosis includes polymorphous light eruption, lupus erythematosus, drug-induced photosensitivity, and photo contact dermatitis. However, solar urticaria may be associated with other photodermatoses, such as polymorphous light eruption and porphyria cutanea tarda.

The diagnosis of solar urticaria is confirmed by photo testing using UVA, UVB, and visible light sources. Sometimes natural light is also used. The aim of photo testing is to determine the spectrum of action (the triggering wavelengths) and the minimal urticarial dose (the minimal dose inducing an urticarial reaction). Determining the spectrum of action is also important for subsequent management so that the patients take precautions to avoid the triggering wavelengths.

The light sources are placed 10 centimeters to 15 centimeters from the back of the patient, and different doses of radiation are delivered. Clinical response is assessed every 10 minutes for an hour. Erythema and wheal occur immediately after photo testing and fade a few minutes after radiation cessation. However, in many cases, photo testing with artificial light sources is not contributive, as it may fail to induce cutaneous lesions, which may be triggered only by natural sunlight exposure. In some cases, repeating photo testing may help to obtain positive results.

A histopathological examination may be performed to rule out other photodermatoses. In solar urticaria, it shows typical features of urticaria which are endothelial swelling and dermal neutrophil, monocyte, and eosinophil infiltration.

Photopatch testing may be beneficial to rule out drug-induced photosensitivity or photo contact dermatitis.

Treatment / Management

There are no guidelines for the treatment of solar urticaria. Different treatments have been used with variable success. Sun exposure avoidance is logically recommended, as well as photoprotection with the use of broad-spectrum sunscreens and dark clothing.

By analogy with idiopathic chronic urticaria treatment, second-generation antihistamine one receptor antagonist agents are largely used and are generally accepted as first-line. These include loratadine, fexofenadine, and cetirizine. They may induce relief in most cases but usually require higher doses, two to four times higher than the conventional ones. 2nd generation antihistamine 1 receptor antagonists seem to have greater efficacy in delayed onset urticaria but no effect on the erythema in solar urticaria.

Since chronically exposed areas seem relatively tolerant to sun radiations, phototherapy (UVA, UVB, visible light) and photochemotherapy (PUVA) have been used to induce tolerance (hardening) to sunlight. This hardening process should be based on the spectrum of action and the minimal urticarial dose. PUVA seems to give a longer-lived response than phototherapy alone.

Intravenous immunoglobulins, plasma exchange, cyclosporine, afamelanotide, and omalizumab have been used in patients with refractory solar urticaria with some success.

Oral steroids, leukotriene receptor antagonists, antimalarial drugs, prostaglandin inhibitors, and oral beta-carotene have shown little or no effect in the management of solar urticaria. Combination therapies are frequently needed to achieve and maintain acceptable clinical relief.

Differential Diagnosis

Differential diagnosis includes polymorphous light eruption, lupus erythematosus, drug-induced photosensitivity, and photo contact dermatitis. However, solar urticaria may be associated with other photodermatoses, such as polymorphous light eruption and porphyria cutanea tarda.

Prognosis

Solar urticaria is an enigmatic disorder that is not well understood. While the diagnosis is simple, its management is difficult. Solar urticaria usually develops in the third decade of life and becomes a chronic disease. The symptoms are managed with a range of treatments, but remission relies on a phenomenon known as "hardening" and is not achieved by all patients. This is the process where continued exposure to ultraviolet radiation decreases the likelihood of attacks. The probability of spontaneous resolution has been estimated as being 15% at 5 years and 25% at 10 years after the onset of the condition.

Overall, the prognosis for patients with severe urticaria is poor. Many patients are restricted indoors and lead a poor quality of life.

Complications

Because solar urticaria is thought to be caused by a type 1 hypersensitivity reaction, severe attacks of solar urticaria can lead to syncopal episodes, bronchospasm, and even anaphylaxis.

Deterrence and Patient Education

As with other conditions that involve photosensitivity, avoidance and protection from UVR must be stressed with patients. Broad-spectrum sunscreen applied liberally to sun-exposed areas, wide-brimmed hats, and clothing that provides adequate coverage from sunlight should be encouraged to avoid attacks of solar urticaria.

Pearls and Other Issues

Solar urticaria often has a chronic course. Approximately half of patients continue to be symptomatic ten to 15 years after the disease onset. A longer duration of solar urticaria before the first medical evaluation, as well as age older than 40 years, are associated with a longer disease course. Patients with exclusive reactivity to visible or natural light seem to have the best prognosis.

Enhancing Healthcare Team Outcomes

Solar urticaria is an enigmatic disorder that is not well understood. While the diagnosis is simple, its management is difficult. The condition is often encountered by the primary care provider, nurse practitioner, dermatologist, and internist. However, because the condition can be difficult to distinguish from other itching disorders, a referral to a dermatologist is recommended.

There are no guidelines for the treatment of solar urticaria. Different treatments have been used with variable success. Currently, high-dose second generation antihistamines, sun exposure avoidance, use of broad-spectrum sunscreens, and dark clothing photoprotection are considered first-line.

Those who fail conservative treatment may be managed with phototherapy and biological agents. Overall, the prognosis for patients with severe urticaria is poor. Many patients are restricted indoors and lead a poor quality of life.