Welcome to icliniq.com.
It could be seborrheic dermatitis or photodermatitis. Allergies may be playing a role. All these are visual diagnosis and the lab tests or biopsies have limited or no role. Seborrheic dermatitis is more commonly present with dandruff and similar rashes on the neck and sometimes upper chest. Photodermatitis would be present over the sun-exposed areas.
In all of these conditions, a mild steroid cream would be useful if applied for a few days. I suggest you to apply Hydrocortisone cream mixed with Ketoconazole for 10 days, twice daily and then switch to plain Ketoconazole for the next 10 days. An antihistamine, like tablet Loratadine, can be taken 10 mg twice daily. Consult your specialist doctor, discuss with him or her and start taking the medicines with their consent. A sunscreen is very important to decrease redness. Apply your sunscreen at least twice daily for example at 8 AM and 12 PM. If dandruff is present, a Ketoconazole-based shampoo may be used twice a week.
You can follow up after two to three weeks.