Photosensitivity

Introduction Photoallergic refers to red spots, pimples or bullous rash on the exposed parts of the skin after exposure to ultraviolet light (such as sun exposure), accompanied by burning and itching. The severity of skin lesions is directly proportional to the intensity, distance and duration of light exposure.

Cause

Many factors (most unknown) can be attributed to light sensitivity, and unless the cause is obvious, each patient with significant photosensitivity must exclude systemic or cutaneous lupus erythematosus. Coloring dry skin disease and certain porphyria diseases can also cause light sensitivity. The most common type of porphyria is late-onset porphyria, which can be sporadic in adults and autosomal dominant inheritance. This porphyria is caused by a deficiency of uroporphyrinogen decarboxylase, which is characterized by increased fragility and the appearance of a millet rash on the dorsal and forearm extension sides. Common facial pigmentation and hirsutism.

Taking various drugs (such as sulfonamides, tetracyclines, thiazides, griseofulvin, psoralen) can cause light sensitivity, although not common, but can occur. Topical or contact with a variety of substances, including cologne and mint-containing perfumes, sulfonamides, coal tars, soaps containing halogenated salicylanilide and certain plants (such as pasture, parsley), can also produce light sensitivity.

an examination

Related inspection

Physical examination of skin diseases Skin color lesions Skin elasticity examination

After sun exposure, red rash, papules or bullous rash appear on the exposed skin, accompanied by burning and itching.

Photoallergies are seen in approximately half of patients with systemic lupus erythematosus, but are not specific for the diagnosis of systemic lupus erythematosus. Patients with systemic lupus erythematosus who are exposed to the sun or exposed to other radiation or artificial light sources such as incandescent lamps may cause erythema on the patient's face to be aggravated, or red rash, papules, or bullous rash may appear on the skin with a burning sensation. , itching sensation, or worsening systemic symptoms.

Differential diagnosis

The photoallergic reaction caused by drugs is mainly caused by the destructive change of the structure of the drug to form an antigen, which causes an allergic reaction to the skin, causing lesions like eczema and urticaria, and even blisters, purple spots, and itching.

Porphyria is caused by a deficiency of uroporphyrinogen decarboxylase, which is characterized by increased fragility of the skin on the back of the hand and forearm and the appearance of a millet. Common facial pigmentation and hirsutism.

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