I think the itch and skin damage is a detox reaction. When the liver can´t detox through the intestines, it sends the toxins back to the blood. That is the enterohepatic cycle. Toxins entering the blood cause the itch. Why the scalp? I don´t know. I mainly have the urogenital area for that. I don´t think it is the magnesium, but K2. I think it has a positive effect on the liver, but the liver can not detox very well. It might be due to some sort of a blockage or because of a metabolic problem with bile. Ketogenic diet causes often the keto itch and rash. Which I think is due to depleted bile. That is why the problem increases with a lot of saturated fat. You can test both supplements separately and see which one it is. Also you can test other detox supplements like activated charcoal, vitamin C or liposomal glutathion to see if there is change. You could also check out the work of Chris Shade and Andreas Moritz of what they have said about detoxing and liver. You could test your bilirubin level as well.