This does seem to be an allergic break-out.It comes under the category of physical allergy.Physical allergies are allergic reactions to cold, sunlight, heat, or minor injury.
Certain drugs are capable of sensitizing the skin
to sunlight. The result is phototoxicity, which appears as an increased sensitivity to sunlight or as localized skin
rashes on sun-exposed areas.
Sunlight, even without drugs, causes immediate urticaria in some people. Shade and sunscreens are necessary.