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Overview of cutaneous photosensitivity: Photobiology, patient evaluation, and photoprotection

Overview of cutaneous photosensitivity: Photobiology, patient evaluation, and photoprotection
Literature review current through: Aug 2023.
This topic last updated: Nov 22, 2022.

INTRODUCTION — Photosensitivity is an abnormal, cutaneous response to ultraviolet radiation and, in some individuals, visible light. One of the key features of a photosensitive eruption is its distribution. In most instances, it occurs on sun-exposed areas of the skin; the face, ears, dorsal forearms, "V" area of the neck, and upper chest are commonly affected sites. However, it can occasionally occur on covered areas of the body, especially in individuals who use tanning beds. Careful clinical evaluation requires a detailed history, including age at onset, timing after sun exposure, duration of the response, and family history, and type of skin lesions that occur. Photodiagnostic and laboratory testing may be necessary to establish the diagnosis. Treatment measures include photoprotection and, oftentimes, immunosuppressive medications.

The principles of photobiology, evaluation of the photosensitive patient, and general recommendations for photoprotection in the photosensitive patient will be reviewed here. The diagnosis and treatment of specific photosensitivity conditions, sunburn, photoaging, and sun protection are discussed separately.

(See "Photosensitivity disorders (photodermatoses): Clinical manifestations, diagnosis, and treatment".)

(See "Polymorphous light eruption".)

(See "Sunburn".)

(See "Porphyria cutanea tarda and hepatoerythropoietic porphyria: Pathogenesis, clinical manifestations, and diagnosis".)

(See "Pseudoporphyria".)

(See "Xeroderma pigmentosum".)

(See "Photoaging".)

(See "Selection of sunscreen and sun-protective measures".)

PHOTOBIOLOGY — Ultraviolet radiation emitted from the sun is divided into three wavelength ranges: ultraviolet A (UVA; 320 to 400 nm), ultraviolet B (UVB; 290 to 320 nm), and ultraviolet C (UVC; 200 to 290 nm). UVC is absorbed by the ozone layer in the atmosphere. Because of this, UVC does not reach the earth's surface and usually does not play a role in inducing photosensitivity. However, it is emitted by germicidal lamps and welding arcs and has been rarely reported to provoke photosensitivity in individuals with occupational exposure. UVA and some UVB penetrate the atmosphere and reach the earth's surface.

Patients with photosensitivity may react to UVA, UVB, or visible light (400 to 760 nm) (figure 1). Longer wavelengths penetrate deeper into the skin. UVA passes through the epidermis and into the dermis, whereas UVB enters into the epidermis, but little reaches the dermis. Ultraviolet radiation has multiple effects on the skin. Notably, ultraviolet radiation causes DNA damage and mutations, which are initiating events in skin carcinogenesis. Ultraviolet-induced immunosuppression may also contribute to the development of skin cancers by interfering with the ability of the immune system to identify and eliminate neoplastic cells before they become clinically apparent skin cancers. A further effect of ultraviolet radiation is the generation of reactive oxygen intermediates, such as singlet oxygen, superoxide anion, and hydrogen peroxide. The generation of reactive oxygen intermediates leads, among other things, to lipid peroxidation, DNA damage, and activation of signal transduction pathways. These effects have been implicated in the pathogenesis of skin cancer, photoaging, and inflammatory responses in photosensitivity disorders. (See "Melanoma: Epidemiology and risk factors" and "Epidemiology, pathogenesis, clinical features, and diagnosis of basal cell carcinoma" and "Photoaging" and "Cutaneous squamous cell carcinoma: Epidemiology and risk factors".)

EVALUATION OF PATIENTS WITH PHOTOSENSITIVITY DISORDERS — Photosensitivity disorders of the skin are conditions in which an abnormal, cutaneous response occurs after exposure to ultraviolet radiation or visible light. The major categories include idiopathic photodermatoses, photodermatoses due to exogenous or endogenous agents, photoexacerbated dermatoses, and photosensitive genodermatoses. A table describing the clinical and diagnostic findings of many of the disorders is provided (table 1). Detailed discussions of these disorders are available separately.

(See "Photosensitivity disorders (photodermatoses): Clinical manifestations, diagnosis, and treatment".)

(See "Polymorphous light eruption".)

(See "Porphyria cutanea tarda and hepatoerythropoietic porphyria: Pathogenesis, clinical manifestations, and diagnosis".)

(See "Pseudoporphyria".)

(See "Xeroderma pigmentosum".)

The initial evaluation of the photosensitive patient involves taking a thorough history and performing a complete skin examination. Phototesting and photopatch testing, as well as laboratory evaluation, are useful in certain cases. (See 'Phototesting' below and 'Photopatch testing' below.)

Patient history — A detailed history should include (table 1) [1]:

Age of onset

Length of time between exposure and the appearance of the eruption

Duration of the eruption

Location of the eruption

Description of the eruption (useful in patients who present without active lesions)

Symptoms (eg, pruritus, pain, burning, and stinging)

Whether the eruption is induced by sun exposure through window glass

Seasonal variation

Tanning bed use

Family history of photosensitivity

Medication history (current and past)

History of products applied to skin (exposure to photosensitizers)

Occupational and recreational activities

Prior history of photoexacerbated dermatoses (see "Photosensitivity disorders (photodermatoses): Clinical manifestations, diagnosis, and treatment", section on 'Photoexacerbated dermatoses')

These features can be used to narrow the differential diagnosis of photosensitivity (table 1). A report of childhood onset may suggest diagnoses such as hydroa vacciniforme, actinic prurigo, or erythropoietic protoporphyria. In contrast, chronic actinic dermatitis typically occurs in adults and in older adults [2].

A complaint of painful skin with sun exposure may suggest a diagnosis of erythropoietic protoporphyria instead of other photodermatoses that are characteristically pruritic. (See "Photosensitivity disorders (photodermatoses): Clinical manifestations, diagnosis, and treatment" and "Congenital erythropoietic porphyria".)

Transient, hive-like lesions appearing within minutes of sun exposure suggest solar urticaria rather than polymorphous light eruption (PMLE). PMLE typically appears hours to days after sun exposure, most commonly as papules and papulovesicles, and persists for days.

A history of reaction to sunlight passing through window glass indicates an ultraviolet A (UVA)-sensitive photodermatosis, because ultraviolet B (UVB), unlike UVA, does not penetrate through window glass. Patients often fail to distinguish between sun exposure and exposure to heat. Care must be taken to establish that ultraviolet, rather than heat, is responsible for provoking the disease.

Review of the patient's past and present medications is important in determining a drug-related cause. Details about outdoor activities, occupation, and recreation are helpful in distinguishing a true photosensitivity eruption from an airborne allergic contact dermatitis, irritant dermatitis, or arthropod bites. Lastly, a history of an underlying disease may bring a photoexacerbated disorder into the differential diagnosis. (See "Photosensitivity disorders (photodermatoses): Clinical manifestations, diagnosis, and treatment", section on 'Photoexacerbated dermatoses'.)

Physical examination — Skin examination should include both sun-exposed and unexposed areas. Photosensitive eruptions typically occur symmetrically on the face, ears, "V" area on the neck and chest, and extensor forearms. Sparing of the relatively shaded area of the upper lip, submental neck, upper eyelids, nasolabial folds, and postauricular areas may be clues for a photosensitive eruption.

Assessment of the type of lesions (eg, urticaria, papules, or vesicles) is essential. Key features for narrowing the differential diagnosis are often available (table 1).

Diagnostic studies — The laboratory studies to be ordered are determined by the suspected photosensitivity disorder, based upon the history and physical examination findings. Laboratory evaluation may include ANA, anti-dsDNA, anti-Ro (SSA), anti-La (SSB) titers and porphyrin studies when lupus erythematosus or porphyria is suspected [3]. (See "Clinical manifestations and diagnosis of systemic lupus erythematosus in adults", section on 'Laboratory testing' and "Porphyrias: An overview", section on 'Approaches to diagnosis'.)

A skin biopsy may provide helpful information but requires correlation with clinical findings. Even in circumstances in which the skin biopsy is nondiagnostic, histology may be helpful in ruling out other diseases included in the differential diagnosis.

Phototesting — Phototesting, if available, can be used to determine a patient's minimal erythema dose (MED). The MED is the lowest dose of ultraviolet radiation delivered to the skin that induces erythema 24 hours after exposure. MED testing is conducted for both UVA and UVB, employing separate light sources.

The MED can be helpful as a diagnostic tool. MEDs in patients with phototoxic reactions and in chronic actinic dermatitis are lower than those in normal controls. Phototesting can also help to determine the wavelengths causing a photodermatosis (UVA, UVB, or visible light). A summary of the results of phototesting in photosensitivity disorders is provided (table 1).

For phototesting, an opaque template with multiple openings and the appropriate light sources are used to irradiate separate areas of skin with progressively increasing doses of UVA, UVB, or, in some instances, visible light [3]. An uninvolved site, typically the back or inner aspect of the forearm, is used as the test area. The lowest dose of radiation that provides uniform erythema over the irradiated site at 24 hours is the MED.

In patients with solar urticaria, the minimal urticarial dose (MUD) is evaluated by administering increasing doses of UVA, UVB, or visible light and assessing the occurrence of urticarial lesions at the site of irradiation within the first hour [4].

In addition to basic phototesting to determine the MED, provocation phototesting may be performed in an attempt to induce lesions. Provocation phototesting is primarily used for suspected PMLE [5] and has also been employed to diagnose photosensitive cutaneous lupus and hydroa vacciniforme [6,7]. The best results for PMLE are obtained when the tested site is in a location of previously affected skin [3]. Radiation doses that approximate the MED typically are administered repeatedly over three to five days [3]. The tested area is subsequently examined for occurrence of lesions. Skin biopsy and histologic examination may be required to confirm the diagnosis.

Prior to phototesting, patients must discontinue glucocorticoids and other systemic immunosuppressants for at least two weeks and antihistamines for at least one to two days [3]. Topical agents, such as topical corticosteroids, should also be stopped one to two weeks in advance.

Photopatch testing — Photopatch testing is useful in patients in whom a topical photoallergen is suspected (photoallergy) [3,8]. (See "Photosensitivity disorders (photodermatoses): Clinical manifestations, diagnosis, and treatment", section on 'Photoallergy'.)

Two identical sets of potential photoallergens are placed on the patient's back. After 24 hours, one set is removed and that site is irradiated with UVA at the dose of 5 to 10 J/cm2. The site is covered again, and 24 hours later, both the irradiated and control test sites are examined for reactions. A reaction to a specific photoallergen in the irradiated site, but not the control site, indicates a photoallergy. A similar reaction in both sites suggests a non-photo-induced allergic contact dermatitis.

Although phototesting and photopatch testing are relatively simple procedures, they are most often performed in specialized centers. (See "Patch testing".)

PHOTOPROTECTION — Effective protection from the sun involves the following:

Avoidance of midday sun (between 10:00 AM and 4:00 PM)

Protective clothing, such as long-sleeved shirts, pants, and broad brim hats

Window films that block ultraviolet radiation for cars and homes

Broad-spectrum sunscreen (protects against both ultraviolet A [UVA] and ultraviolet B [UVB])

Sun avoidance and protective clothing should be emphasized as important measures of photoprotection for patients of all skin types who have photosensitivity disorders [9]. Sunscreen alone is not sufficient and should be used as an adjunct to other methods of sun protection [10-12].

For patients who are sensitive to radiation in the UVA range, it should be noted that substantial amounts of UVA are present in the morning and late afternoon, as well as midday. Because UVA can penetrate window glass, the very photosensitive patient may even have difficulty indoors and in a car. Window films that block UVA and some visible light can be purchased for use in cars or homes [13].

Protective clothing, such as long sleeves and broad brim hats, should be worn while outdoors [14]. Fabrics that are tightly woven, thick, or dark-colored are useful for protection [15]. Clothing developed for photosensitive individuals is commercially available from specialty companies. Clothing treated with broad-spectrum ultraviolet absorbers is also available. (See "Selection of sunscreen and sun-protective measures", section on 'Photoprotective clothing'.)

Daily use of broad-spectrum sunscreens with a minimum sun protection factor (SPF) of 30 are important for patients with photosensitivity, particularly those with photosensitivity in the ultraviolet range. Sunscreens are divided into organic (chemical) and inorganic (mineral) products (table 2) [16]. Organic sunscreens provide protection in the ultraviolet range; inorganic sunscreens have the ability to block both ultraviolet radiation and some visible light. In some situations, protection against visible light is needed. For this, tinted sunscreens can be effective [17]. (See "Selection of sunscreen and sun-protective measures", section on 'Types of sunscreens'.)

The effectiveness of sun protection depends on the severity of photosensitivity and how well patients adhere to sun protective guidelines. Patients with more severe cases of photosensitivity may not respond to sun protection alone and will likely require other treatment modalities, depending on their specific diagnosis. (See "Photosensitivity disorders (photodermatoses): Clinical manifestations, diagnosis, and treatment".)

SUMMARY AND RECOMMENDATIONS

Definition – Photosensitivity is an abnormal response to ultraviolet radiation or visible light that underlies many different cutaneous disorders termed "photodermatosis." The action spectra implicated in photodermatoses include ultraviolet and visible light.

Diagnosis:

History and skin examination – The diagnosis of a photosensitivity disorder is primarily based upon obtaining a history and performing a skin examination. The age of onset, timeline of the eruption, family history, medication history, and appearance of the lesions are invaluable for narrowing the differential diagnosis (table 1). (See 'Patient history' above and 'Physical examination' above.)

Laboratory tests – Laboratory evaluation may include ANA, anti-dsDNA, anti-Ro (SSA), and anti-La (SSB) titers and porphyrin studies based upon a clinical suspicion of lupus erythematosus or porphyria. Skin biopsy can be helpful when correlated with clinical findings. Phototesting to determine the minimal erythema dose (MED) and action spectrum can narrow the differential diagnosis. Photopatch testing is useful in patients in whom a topical photoallergen is suspected. (See 'Diagnostic studies' above.)

Photoprotection – Photoprotection via sun avoidance and sun-protective clothing is essential. Broad-spectrum (ultraviolet A [UVA] and ultraviolet B [UVB]) sunscreens are useful but may not adequately protect patients when used alone (see 'Photoprotection' above):

Broad-spectrum (UVA and UVB) sunscreens with a minimum sun protection factor (SPF) of 30 provide protection for patients with photosensitivity in the ultraviolet spectrum. Products containing photostabilized avobenzone or ecamsule offer improved protection against UVA. Sunscreens that contain nonmicronized zinc oxide and titanium dioxide also provide broad-spectrum photoprotection (table 2). (See 'Photoprotection' above.)

Sun avoidance and photoprotective clothing provide primary protection for patients with visible light sensitivity. When skin exposure to sunlight is unavoidable, physical blocker sunscreens (titanium dioxide or zinc oxide) in an opaque, nonmicronized formulation and tinted sunscreens can provide visible light protection. (See 'Photoprotection' above.)

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