Cinnamon is a commonly available spice that has recently become popular for treating diabetes and other health conditions, although little evidence is available to support its use. While cinnamon is generally safe and well-tolerated, the use of highly concentrated cinnamon capsules can increase the risk of side effects. As with any health supplement, you should consult your doctor before taking cinnamon capsules to treat a medical condition.
Exposure to cinnamon has been reported to cause skin irritations, such as skin rash. When applied to the skin, cinnamon may cause contact dermatitis. In at least one case, oral cinnamon supplements have been reported to worsen rosacea, a chronic skin condition characterized by inflammation and redness of the nose, cheeks, eyelids and forehead, explains an article published in the June 2008 issue of the "Journal of Drugs in Dermatology."
Cinnamon supplements can sometimes cause constriction of the airways, particularly the bronchi, according to the University of Michigan Health System. Cinnamon has also been reported to cause blood vessels to widen, also known as vasodilation, notes the "Journal of Drugs in Dermatology."
The use of oral cinnamon products, including gum and toothpaste, is frequently associated with a variety of oral side effects, such as inflammation of the mouth, also called stomatitis, reports the Memorial Sloan-Kettering Cancer Center. Oral cinnamon products have also been reported to cause gingivitis. The risk of these side effects is increased by long-term use of the products. Long-term ingestion of concentrated cinnamon oil has also been reported to cause inflammation of the mouth.
Cinnamon contains chemicals that can possibly damage the liver, and long-term use of high doses of cinnamon supplements may cause liver damage, particularly in people with existing liver disorders. Cinnamon can also affect blood sugar levels, and people taking medication to control blood sugar should use caution when taking cinnamon supplements. Patients with hormone sensitivity disorders should also exercise caution when taking cinnamon, because cinnamon has been demonstrated to possess estrogenic activity and could possibly worsen certain hormone imbalances.