Yesterday I was potting a plant. My leg was in the partial sun. When I went to have a shower, preparing to go out to a lunch, I found a reddish lacy rash across my right thigh. It was slightly hot and 'uncomfortable' feeling - I realise that is not very specific.
I went to lunch, and had a nice time. Coming home I became chilled and wrapped myself in a blanket on the sofa. When that didn't work, I put on wool leggings. After a while although I still felt chilled, my leg felt hot and scratchy and uncomfortable again.
Over the next couple of hours the feeling increased with a general discomfort. Finally I noticed mild nausea and a slight headache and took some aspirin. About 30 minutes later, the various discomforts eased slightly.
Livedo reticularis is the purplish/blueish lacy rash that comes out when its cold. It can be benign in slender young women but in extreme cases its a sign of various auto-immune syndrome (lupus and Hughes disease being high on the list, with RA) but MS was not mentioned.
Erythema ab igne is the reddish/purplish lacy rash that comes out when its hot. Direct application of heat is the culprit, usually infrared heat. I do get it a little sometimes if I over-heat or over-apply my hot bag.
I do get both. I find it most significant that I get them on the right thigh, where I have other issues, rather than anywhere else much. They're not permanent, yet.
They join the list of skin conditions I already get: pityriasis, dermatitis, prickly heat, and, when I'm really lucky, boils.