Hives, or Urticaria, are caused by your body's immune system when it doesn't like something. So like once in a while your body is super dumb and it decided to over react to something that normally is just fine, these reactions are called hypersensitivity reactions or more commonly allergic or anaphylactic reactions. Hives are part of this. Along with the T-Cells and B-Cells your body uses Histamine to help combat intruders. Histamines are one of the chemicals that causes swelling in your body aka the bodies inflammation response. When you have one of these over-reactions, your body starts pumping these out like crazy cause again your body is dumb. When histamines hit their receptors it triggers that swelling response. This can be really bad like when it affects the airways but when they trigger in the capillary beds, it causes them to dilate and allow fluids to seep into the surround tissue giving you those welts. That's the main player but there is a lot of other stuff that helps by changing the permeability of cell walls etc but Histamines are your main culprit.

Wow! Dang! Thanks so much for this. Can I ask you - are there any autoimmune diseases that would cause this? What about broken capillaries visible on the body?

Just to be truthful up front I ain't a doctor. Been an Army Medic for some years and an AEMT so take what ever I say with a grain of salt lol. But a lot of autoimmune disorders have hives as a potential symptom, such as thyroid diseases, arthritis and even diabetes. Anytime those small vessels dilate they can potentially burst. But both hives and burst capillary's, which is called Petechiae, are pretty common in a lot of different diseases. You can get those with out having a true autoimmune disorder as far as I know.

Ah thanks. Interesting. I’ve been on a wild medical journey the past five years. Have been to so many specialists and still have no answers. My blood work shows high levels of eosinophils and I am ANA positive. Have had worsening broken capillaries for about five years - started on face and now down to chest. Hives and severe itching started within last few months/weeks.

Ooof dude that's way above my wheel house. I got basics down but no where near that level of knowledge. I liked your original post cause I tell new Medics the same thing! I did work in a OR for a while and from experience ANA positive is super indicative of autoimmune but any more then that I'm clueless. I'm sorry about all that brother, it insane we know so much and so little that "medical mysteries" still exists. All the best wishes, when you get better here soon, come reply and lmk!

Thanks man. And thanks for your service in the army!