Typed a reply last night but it never showed up. Weird.
There is a condition fairly recently named called Mast Cell Activation Syndrome or MCAS that you should look in to, and it commonly coexist with POTS and EDS. It is basically when mast cells that the immune system stores pre-made chemicals in get triggered to dump their contents (degranulate) inappropriately. The process acts quite differentry from traditional allergic reactions, and most of the time triggers won’t show up on traditional allergy testing. Stomach pain is quite a common symptom, uv sensitivity less common but I’ve heard more than a few patients mention it. There are a myriad of different skin reactions I’ve seen described. Other common reactions are flushing, hives, swelling, blood pressure goes high or low or fluctuates between, headaches, and quite a few suffer anaphylaxis with throat closing/swelling or loss of blood pressure and need epi pens for this emergency situation. There is no clear explanation of how MCAS gets kicked off, some like me have had symptoms since childhood but got worse suddenly at some point, others it’s out of the blue and suspected to be from insect venom, viruses, powerful antibiotics, etc. Common triggers are alcohol, insect venom, nsaids, opiates, antibiotics, fragrances/smells, foods, various medications or the fillers or colors in them, stress, weather, and the list goes on.
Treatment is usually antihistamines to block the cascade of histamine released from the mast cells, you will see references on this site to zantac+zyrtec being a good starting point to try. There are also mast cell stabilizers that help keep the mast cells from degranulating.
Since you are going to a dermo, you could start with asking for testing for mastocytosis, which is a related condition but consists of the body over producing mast cells. It is more rare than MCAS, but must be ruled out. Most dermo’s should be at least a little familiar with mastocytosis since the disease often includes skin involvement. First test is generally a blood test for Tryptase, a high level would point to possible mastocytosis. You could ask the dermo to biopsy any spots that regularly itch or swell up and ask for them to be specifically stained to look for mast cells.
It’s tough to be concise with this info, but there are now many resources out there. Tmsforacure.org is the US Mastocytosis Society site, mastocytosis.ca is the Canadian site. Feel free to ask me any questions, I’m a moderator on one of the Facebook groups.