Cinnamon: That tingling sensation is the cinnamon burning your skin. Avoid. It’s become trendy to tell people to use this as an all natural ingredient that magically re-grows lost unicorn horns, because the tingle makes people feel like it’s working, but it’s not. It is classified as an irritant for a reason, and it’s highly allergenic (i.e. that swelling is caused by histamines and can cause permanent disfigurement).