This could be a condition called Polymorphous Light Eruption (PMLE), which is a hypersensitivity to the sun.
This condition is most commonly triggered by springtime sun exposure. The rash only forms on sun-exposed parts of the body, usually 1 to 4 days after exposure. The sensitivity of the skin and the severity of the rash gradually lessen as spring changes into summer and the skin becomes adjusted to ultraviolet rays.
The rash is non-specific, red blotches appear that may be raised, bumpy or hive-like.
Because the rash is so nonspecific, its presence limited to only on sun-exposed areas is a very important diagnostic feature.
A skin biopsy might be in order to confirm the diagnosis of PMLE. Itching is the main symptom, so the treatment is with OTC anti-histamines like Cetrizine. Other OTC remedies for soothing discomfort include anti-itch preparations like PrameGel and Aveeno Oatmeal Anti-itch Concentrated Lotion.
If the rash doesn’t improve as the summer progresses you may want to pursue a more in-depth work-up to rule out auto-immune disorders like SLE.