Thank for your reply.
I wanted permission to answer your query and hence I asked.
From your history and the rash , it does indicate that you have an autoimmune in nature rash called Polymorphous light eruption, also known as polymorphic light eruption. This is an itchy rash caused by sun exposure or radiational in people who have developed a sensitivity to sunlight. The rash usually appears as red, tiny bumps or slightly raised patches of skin just like how you have got.
I would suggest you should get a skin patch test or a photosensitive patch test done to prove it.
The biopsy as you have mentioned above is normally not specific and is indicative of allergy.
This can be treated with the use of a good physical block sunscreen daily in the morning .
Use of Aveeno Skin relief moisturiser at night.
In take of beta Carotene supplements once a day for 3 months to reduce the photosensitivity.
You should use a prescription cream called tacrolimus 0.1 % on the area twice a day for 10 days or more till the area heals. This is a non steroidal approach.
Do not use steroids on the skin for long periods of time.
Please do let me know if you have any further queries.