I've already posted in undiagnosed symptoms but figured it might fit better here. Recently, in the past year or so, I have noticed the skin on my legs turns red when exposed to heat for long periods. It is in a constant pattern but goes away after a while. It doesnt need to be an extreme amount of heat either, for example I can just be sitting in a stationary car on a sunny day and if light shines through the window onto my leg after around 5-10 minutes the skin becomes red. It isnt accompanied by pain, itchiness, inflammation or texture, it just becomes red. This isnt much of a problem but my knees sometimes can heat up after walking and this in turn makes my knees red. Its more of an annoyance than anything but I would like to know what's going on.