Dr. Roman wrote at 2016-02-20 23:56:05
It's a circulation phenomenon involving the capillaries, which can turn on and off like a button. Men shave their faces with a hot towel before the shave and a cold rinse after to control the opening and closing of pores to expose hair for cutting and then close it up as the skin pulls away from cold water and shunts thick blood towards the center of the body to prevent heat loss and keep out of zones that would cool and thicken blood, especially at a time of low metabolic need for oxygen (lower temperature = less energy and oxygen need) in that small tiny area controlled by a capillary. This happens rapidly to accommodate for sexy naked time in the winter and hot tub parties where the drinks alone can cause flushing by opening the skins capilarries (think red-nosed alcoholics or light-weight drunks with hot ears and facial flushing). So you see, these examples provide some insight on just how fast tissue in the skin adapts to temperature and the environment. Similarly with allergic responses, though in a different way using the immune system to trigger swelling and inflammation, which we of course put a quick stop to with immediate icepacks before it can happen. Another example, though more related to deeper tissue injuries. Still the allergic responses of the skin can be rapid, like full body rash and swelling including airways of the throat closing up. Some extreme cases are fatal and immediate adrenaline injections require "epi-pens" at all times to stop the reaction. Now if you want fast skin changes, that will do it. Closes those capillaries directly and opens large vessels of the brain and heart instead.
You happen to have this problem, or HAD this problem by now, because you were dehydrated from a bad cold. Besides that, viral infections directly and indirectly through the immune cells reacting to them shift the fine-tuned controls of the skins "redness/paleness" AKA capillary blood supply to our exterior surfaces and areas next to each other may have completely different effects taking place at the time, leaving a pattern on the surface of the skin, alongside the already low pressure and dehydrated state. We always pale with pressure but in this circus going on in the skin, capillaries don't quite "spring back" the way they normally would, leaving pale spots and slow circulation. We literally call this "capillary refill" and test it on patients' fingernails to determine if they need more water in their arteries. More pressure and volume to fill everything up. First goes the skin, next the vital organs so its no laughing matter when a very sick patient has a white thumbnail requiring a lot of time to return to its usual hue. You had this in a similar way but the severity was typical of an unusual viral cold for you.
I hope this explains the mechanisms of your rash that day and provides a clearer picture. It's not a generic response. Quite the opposite. It targeted subjects that I felt you were reaching for to be satisfied with your answers. Did it do the job?
Jon wrote at 2016-07-12 19:58:31
Did you ever get to the bottom of this? I have the EXACT same thing that happens to me.