Frankincense has been used for centuries in religious ceremonies, but there are some potential side effects to using it. Its use may cause asthma-like symptoms such as coughing, wheezing and difficulty breathing in people who are particularly sensitive to the oils found in frankincense. Additionally, if applied topically or taken internally, frankincense can cause nausea, vomiting, and diarrhea. It's best to consult with a healthcare professional before using frankincense for any purpose.