Blisters on skin immed after being in sun, also becomes physically ill

Ok no idea where to start with this so I will just explain, my youngest daughter has always had issues from sun exposure, she has never been able to be exposed to the sun for more than 10 minutes at a time.  when she was little she would scream when the sun hit her, she does use spf 50 every single day, however, things have gotten a lot worse.  she has always gotten an immediate rash by immediate I mean within less than a minute especially on her arm and face.  Our insurance requires a referal for a dermatologist we are now on the waiting list but things are getting much worse. even though we are still getting snow off and on so the sun is limited she is having major rashes with even minimal exposure, she is 18 now btw,she says it feels like it did when she had third degree burn on her wrist,but feels like that all over her body and she also says it itches like crazy. Also if she is exposed to the sun for anymore that 5 maybe 10 minutes she will spend a week in bed with extreme headaches and vomiting. I am just trying to find answers as to what this could be, her doctor is thinking she is allergic to the sun we have always had to keep things dark in our home or it would make her sick if to much sunlight came in, this doctor she is seeing now is a general prac.  we are on the waiting list for a dermatologist so in the meantime since there is a 6 month plus waiting list we have to wait to find out what to do to help my daughter.  Of course limited sun exposure but any ideas if this could actually be an allergy?  Why are the symptoms just intensifying as she gets older, it seems the more she gets sun exposure wise the worse the next attack is.  any ideas to help her until she can see the dermatologist would be amazing, any ideas what this could be? thanks in advance.

[Dr J Singh]

Hello,
From the symptoms it looks like your daughter had solar urticaria or solar allergy. It is the development of hives minutes after exposure to the sun, which resolve in less than 1 hour.

Ask your daughter to apply a good sunscreen with minimum spf 30 atleast half an hour before going out in the sun. She 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. She 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.

Please discuss this treatment option with your dermatologist.
I sincerely hope that helps. Take care and please do keep me posted on how you are doing.