Sun Allergy and Photodermatoses

“"Sun allergy" is an umbrella term used in everyday language. Medically, abnormal reactions triggered by sunlight or artificial light are classified under the heading of photodermatoses, and they are not all the same disease.

Polymorphic light eruption (PMLE) is one of the most common idiopathic photodermatoses. It typically develops as itchy papules/plaques in sun-exposed areas within hours or days, usually in early spring or summer. Attacks often appear similar in the same individual and may decrease in some patients due to natural hardening as the summer progresses.

Solar urticaria is different: urticaria plaques can develop within minutes of UV or visible light exposure. PMLE and solar urticaria are distinct diseases in terms of timing, clinical presentation, and immune mechanisms.

Phototoxic reactions to drugs or chemicals are similar to exaggerated sunburn; they do not require prior sensitization. Photoallergic reactions, on the other hand, appear more eczematous due to delayed-type immune mechanisms. Some drugs, such as doxycycline, are associated with phototoxicity; however, these drugs should not be discontinued without a doctor's recommendation.

Diseases such as lupus and some porphyrias can also be triggered by light. If there are blisters, scarring, significant systemic symptoms, or unusual photosensitivity, one should not simply assume "sun allergy.".

History, distribution, and timing are essential in diagnosis. Phototests, photoprovocation, photopatch tests, classic patch tests, laboratory tests, or biopsy may be used in necessary cases. Photopatch tests are particularly used in the evaluation of photoallergic contact dermatitis.