Hi, I am not sure either but wanted to say hello. Could there be something in the sunscreen you are using that you may be allergic to? Just a thought. Am sure others will stop by, too with ideas.
This can be due to solar urticaria. Apply a good sunscreen with minimum spf 30 atleast half an hour before going out in the sun. You can take non-sedating antihistamines such as Cetirizine or Loratadine(Claritin) when the rash appears. Short courses of oral cortisone or steroids are taken for short periods (one to three days) to settle more severe symptoms. You may take Vitamin C along with the prescribed treatment. Vitamin C is a general anti-allergy supplement. Also apply calamine lotion and a mild steroid cream like dermacort on the rash.
To prevent solar urticaria in future, desensitization using phototherapy and photochemotherapy are often advised. In this we try to decrease the amount of exposure by gradually increasing exposure to the form of radiation that brings about the reaction.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.