Whenever a cell is in danger (as, for instance, from a mosquito bite!), the cells that are in danger emit histamine. That wonderful hormone has the ability to send a message to those places in the body which change the blood flow -- to send more blood (water) to that area to provide the nutrients needed to heal the problem, and to carry away the toxins. So, when a mosquito bites you, the area around the bite itches and swells. That is the action of histamine coming to the rescue -- bringing extra blood to supply nutrients to the cells that have been poisoned by the mosquito bite, and to carry away the poison. When a cell is completely overwhelmed (as when it is loaded with toxins) it is in such apathy that it can't even release histamine -- in other words, it is so sick that it can't even call for help. Now, take a look at those cells near the capillaries. They are often loaded with toxins and there is never enough blood flowing near them to take the toxins away. Now, put some niacin in your body and he capillaries increase in size. How much? I don't know exactly, but often at least double in size. Now, you have two blood cells going through the capillary, side-by-side. The chances that this increased blood flow can take away some of those toxins is at least double what it had been. As those poor cells start coming back to life -- getting rid of toxins, they rise UP to the level where they can send out calls for help. They send out small quantities of the hormone, histamine. Histamine causes an itchy feeling anywhere it goes. It also causes the body to send more water (blood) to that area, but what YOU experience is the red skin and the itchy reaction from histamine. If you take niacin and DON'T have a flush, it could be that your capillaries are too far gone to be helped, or more likely, you don't have a lot of toxins ready to be removed just then. So, you should seek the niacin flush. It does a great deal of good for your body -- increasing blood flow, taking nutrients to areas that are starved, and taking AWAY some of those toxins that cause illness, tiredness and disease.
When I was in high school, I knew a few savy pot heads that Niacin flushed a bunch of times to pass drug tests. I do not know if this works but they did it repeatedly. Much like most accidental discoveries, some of these kids noticed that within 24 hours, there skin (acne/complexion) had cleared entirely. Now I am not sure how niacin affects PDG2, but I can personally vouch for the benefits I bolded in this article. I have severe allergies, and I get the same reaction during an allergy attack that I do with a niacin flush, just less severe. The silver lining here is that because are scalp is the furthest region from our scalp upwards, It certainly gets the least blow, and this creates a back up of toxins localized in the scalp and skin. I have also experimented with Niacin for acne a few years back, and I can say without a doubt this has a severe effect directly to the skin, and I would believe that a two pronged effect is responsible. 1. Niacin dilates capillaries allowing them to release toxins and fill with blood, and it also causes the body to go into protection mode and send an abundance of nutrients to the skin. I would have to believe that this would be very positive given most people are trying to flush roaming DHT from Telogen Effluvium blood, and increase scalp circulation.