When I transitioned to a fully raw diet, I got one on my shoulder I assumed was from detox. Disappeared in about a week.
Boils are not usually a sign of kidney disease. In rare cased detox, but in more common cases it is just an infected hair or pore that may have gotten big. Think of a big zit.
If it stays more than a week or two, then see a doctor to rule out conditions like diabetes.
Dietary causes and fixes:
High oxalate foods can cause skin eruptions. You may want to focus on a low oxalate version of any diet you choose and avoid spinach, kale, chard, grains in large amounts, and potatoes in large amounts.