The photodermatoses are a group of cutaneous disorders characterized by an abnormal reaction to light exposure.

The photodermatoses comprise many different disorders that have in common an abnormal reaction to light exposure. Exposure includes both sunlight and light from artificial sources (e.g., tanning beds, lasers and other light-generating devices). The differential diagnosis includes both the photodermatoses and other conditions that may mimic them because they involve areas of skin exposed to natural or artificial ultraviolet (UV) light. These include allergic contact dermatitis due to airborne allergens and other eczematous eruptions that are exacerbated on exposed skin.

The differential diagnosis for the photodermatoses themselves include chronic actinic dermatitis, polymorphous light eruption, chemical and drug-induced photosensitivity, photoexacerbated dermatoses (such as lupus erythematosus), actinic prurigo, solar urticaria and hydroa vacciniforme.

In evaluating a patient and developing a differential diagnosis, it is helpful to understand the different types of reactions. Abnormal reactions to UV exposure can be due to either an abnormal response of the skin or involve some drug or chemical that causes photosensitivity.

Abnormal response of skin to UV exposure can be divided into the following 4 types **

** Listed in approximate order of commonness. Incidence may vary depending on latitude and racial factors.

  • Immunologically mediated, previously known as idiopathic

  • Dermatoses exacerbated by UV exposure

  • Defect in DNA repair disorders

  • Drug-induced and chemical-induced

Immunologically mediated:

  • Probably have a genetic and immunologic basis.

  • Includes polymorphous light eruption (PMLE), actinic prurigo (AP), juvenile spring eruption, solar urticaria, chronic actinic dermatitis (CAD), and hydroa vacciniforme (HV). **

Dermatoses exacerbated by UV exposure:

  • This includes a broad range of cutaneous and systemic disorders. The most common conditions where photoexacerbation frequently occurs are rosacea, herpes simplex labialis, and lupus erythematosus. It has been reported to occur with acne, atopic dermatitis, psoriasis, blistering disorders (pemphigus and pemphigoid), dermatomyositis, lichen planus, nutritional deficiencies, and cutaneous T-cell lymphoma (CTCL).

  • Paradoxically, phototherapy with PUVA (psoralen plus UVA), narrowband UVB (NBUVB), intense pulsed light (IPL) or excimer laser maybe used as treatment for many of these conditions (e.g., acne, psoriasis, eczema, lichen planus, and CTCL).

Defective DNA repair:

  • A group of uncommon to rare inherited disorders where patients lack the ability to repair DNA damaged by UV exposure.

  • These are readily identifiable by their early age of onset and characteristic features.

  • Includes xeroderma pigmentosum (XP), Bloom syndrome, Kindler syndrome, ataxia-telangiectasia syndrome, Rothmund-Thompson syndrome, Cockayne syndrome, trichothiodystrophy, and UV-sensitive syndrome. **

Photosensitivity to drugs and chemicals:

  • Exogenous:

    These photodermatoses are due to drugs or chemicals that are either ingested or come in contact with the skin. The reactions are either toxic or allergic in nature. These are transient in nature.

    Phototoxic reactions appear as an exaggerated sunburn and are usually due to drugs. In severe cases, blistering may occur.

    Photoallergic reactions are often eczematous with redness, scaling and occasionally blisters. Contact with topical medications and other chemicals, including those present in certain plants, is the most common cause although some drugs may cause photoallergy as well. The most common drugs and other agents are listed in the tables below.

    A large number of drugs are capable of producing phototoxic reactions and some, such as doxycycline, are dose-related. The most common drugs are listed in the tables below. See Table I and Table II.

  • Endogenous:

    The porphyrias with cutaneous manifestations are the most common cause.

    These eruptions have characteristic features and are chronic.

Table II.


To create an appropriate differential diagnosis, one must first take a careful and detailed history as patients are usually unaware of what they did to cause their condition. One needs to ask when the eruption first began and whether it is intermittent or chronic. If intermittent, the duration of the attacks can be a clue to diagnosis. Age of onset is important to ask, as some photodermatoses commonly present in certain age groups. For example, actinic prurigo, erythropoietic protoporphyria, and congenital erythropoietic porphyria have a childhood onset. Does the patient have any significant family history? Are there any systemic abnormalities? Visceral and neurologic abnormalities may indicate one of the porphyrias. Special attention needs to be given to any medications or supplements the patients are taking. Foods, topical medications, and skin care products are also important. Does the patient have any exposures to chemicals in the home or workplace? Attention needs to be paid to cutaneous symptoms. Are the eruptions itchy, painful, or burning?

A careful examination of the skin will give clues as to possible cause. To begin, one must first determine whether the patient’s eruption is actually related to light exposure or due to some other cause. Although the eruption may be present on skin not covered by clothing the affected areas may have been exposed to airborne agents or the patient may have come into contact with an irritating agent or allergen. For example, a person allergic to poison ivy might have been exposed to smoke from burning brush. In such a case, the eruption usually affects all exposed skin.

In the photodermatoses, certain areas such as inner aspects of the upper arms, are typically protected from sunlight exposure. While the photodermatoses are predominantly seen on areas exposed to light, covered areas may occasionally manifest the eruption as well. The appearance of the eruption is obviously important. Is there only erythema or are papules, blisters, erosions, wheals or scaling present? Is there any scarring or pigmentary change? In some cases, there are no visible eruptions but only itching or pain.

While the diagnosis is usually made on the basis of the history and physical examination, certain tests may be confirmatory or help in the identification of the causative agent.

  • Antinuclear antibodies and other immunologic testing can help to confirm lupus erythematosus and distinguish SLE from rosacea.

  • Porphyrin levels can help to confirm the diagnosis of porphyria. Complete porphyrin profiles, including erythrocyte, urine, and stool porphyrin levels, distinguish the different types.

  • HLA typing may be helpful in actinic prurigo (strong association with DR4, subtype DRB1*0407).

  • Genetic studies are useful to differentiate inherited disorders with defective DNA repair.

  • Biopsies for histologic examination and immunoflourescence are very helpful as many of these disorders have a characteristic histopathologic pattern.

  • Photopatch testing can often identify the allergen in photoallergic dermatitis.

  • Phototesting is helpful for confirming the presence of a photosensitive disorder and is most helpful for the diagnosis of immunologically-mediated photodermatoses. The uninvolved skin of the back or abdomen is exposed to varying doses of UVA, UVB, and/or visible monochromatic or broad-spectrum radiation. Twenty minutes after the exposure, a first reading to detect urticarial lesions is done, which would be present in solar urticaria. Then the MED, which is defined as the lowest dose of UVA or UVB that will produce perceptible erythema over the exposed site, is determined 24 hours after the exposure. Provocative light testing is a form of phototesting that involves exposing the same site for up to 3-4 consecutive days. This is used to reproduce an eruption that can be examined in greater detail. Provocative light testing is not commonly performed but can be used to confirm a diagnosis of polymorphous light eruption (PMLE). It can also be useful to confirm photosensitivity in lupus, although it will be negative in other photoaggravated conditions.

Appearance of UV exposed skin:

Confluent Erythema +/- Other Lesions

  • Patient is taking a drug or supplement known to cause photosensitivity: Drug Induced Photosensitivity

  • Elevated erythrocyte protoporphyrin levels: Erythropoietic Protoporphyria (EPP)

  • Infant: Sunburn. If excessive, exclude XP

  • Patient has an underlying photoexacerbated dermatosis: Lupus Erythematosus and others

Intermittent, Patchy Erythema +/- Other Lesions, Usually Itchy, Patchy or Burning

  • Erythema and usually wheals within minutes of UV exposure and lasting for an hour or longer: Solar Urticaria

  • Erythema with itching, papules +/- vesicles and edema, within hours to days of UV exposure and lasting for hours to days:

    – No scarring: Polymorphous Light Eruption (PMLE)

    – Scarring: Hydroa Vacciniforme (HV)

  • Erythema with itching and/or pain

    – Erythema +/- vesicles or wheals. Onset within minutes, lasts for an hour or more: Phototoxic reaction to topical drug or chemical agent

    – Erythema with scaling +/- blisters, onset within hours, lasts for days: Photoallergic reactions to topical drug or chemical agent

  • Erythema with scaling: Photoaggravated dermatoses (often seborrheic dermatitis)

  • Erythema with pigmentary change and mild scaling: Photoaggravated dermatoses (especially cutaneous forms of lupus erythematosus)

  • Erythema, edema and or erosions with immediate burning sensation: EPP

Persistent Erythema +/- Other Lesions In Specific Areas, Usually Symmetric

  • Erythema +/- papules and scaling over malar areas: Systemic Lupus Erythematous and Rosacea

  • Erythema +/- papules and scaling over central forehead, nose, malar areas and chin: Rosacea

  • Erythema with blisters, erosions, crusts. Hypertrichosis, milia, hyperpigmentation and scarring often present: Porphyria Cutanea Tarda (PCT)

Persistent Erythema With Other Lesions

  • Papules and/or vessicles: Actinic Prurigo (AP)

  • Scaling, plaques and/or nodules: Chronic Actinic Dermatitis (CAD)

Intermittent Itching or Pain With No or Minimal Skin Changes

  • Painful, onset within minutes, lasts for hours. Elevated erythrocyte protoporphyrin: EPP

  • Itching, onset within minutes, lasts about an hour: Mild solar urticaria or mild aggravation of underlying photoaggravated dermatosis

With the exception of tests and studies described above, no other tests typically useful in making the diagnosis.

1. Strict photoprotection should be enforced and is considered first-line therapy.

  • Seeking shade during peak daylight hours, this is 10 A.M.-2 P.M. for UVB and throughout the day for UVA.

  • Sun protective clothing is available. For children with XP, special protective garments are available through local XP patient support groups and are essential for reducing the risk of developing skin cancers.

  • Broad-spectrum sunscreens, protecting against both UVA and UVB exposure, are helpful in all photodermatoses. A sun protection factor of at least 30 is recommended. For patients with photoallergic reactions to sunscreen agents, a physical sunblock containing zinc oxide and/or titanium dioxide can be used, as well as protective clothing. Many companies manufacture SPF-rated garments.

  • UV blocking films can be place on home and car windows.

2. Oral beta-carotene is used for treatment of EPP and may be helpful in other photodermatoses as well.

3. Underlying photoaggravated dermatoses such as lupus and porphyria should be treated appropriately.

4. Discontinue any offending medications or topical preparations that are exacerbating phototoxic or photoallergic reactions.

5. Antihistamines are useful in relieving the itching associated with pruritic photodermatoses.

6. Topical and occasionally systemic corticosteroids are used for symptomatic relief in most photodermatoses. Topical tacrolimus has also been used with some success.

7. NBUVB and/or PUVA are helpful in treating PMLE, AP, HV, and solar urticaria.

8. Refractory cases of actinic prurigo may respond to thalidomide.

9. Resistant cases of CAD and HV have been treated with antimalarials, cyclosporine, mycophenolate mofetil and azothiprine.

Although the different photodermatoses have specific and characteristic presentations, diagnosis is not always easy as there are many overlapping features. Rosacea and SLE can often have a very similar appearance both clinically and histologically. As the name implies, PMLE has a variety of clinical expressions. As many as 50% of patients with lupus erythematosus have cutaneous findings compatible with PMLE. Drug-induced pseudoporphyria (due to NSAIDs, especially naproxen) may be clinically indistinguishable from PCT.

Treatment can be difficult. Photoprotective measures (sunscreens, sunblocks, protective clothing and window films) are helpful but do not completely prevent exacerbations. Antihistamines and topical corticosteroids provide some symptomatic relief. Systemic corticosteroids and other immunosupressive agents have potential serious side-effects. Systemic agents may be required to control the disease. These include antimalarials, dapsona and methotrexate as well as anti-inflammatory agents such as nicotinamide.

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