Camphor, the main active ingredient in Vicks Vaporub, is a terpene that has been used in medicine for centuries to numb pain, improve blood circulation, and clear the nasal passages. When applied topically, camphor produces a cooling sensation that helps to alleviate localized pain. Research shows that although camphor is less effective at relieving pain than capsaicin, its effects take hold much quicker, making it useful for anyone in need of immediate relief. Aside from reducing pain, camphor can also be used to improve blood flow. One study completed in 2014 demonstrated that patients who applied camphor directly to the skin increased blood circulation in both their skin and muscle. Because camphor is the main active ingredient in various nasal decongestant medications, it's easily assumed that this terpene is an effective nasal decongestant. Unfortunately, this is not technically correct. Research demonstrates that inhaling camphor vapors does not improve nasal resistance to airflow. Instead, the cold sensation in the nose improves perceived nasal airflow. This means that while camphor does not help patients breathe easier, it tricks them into believing that it does. Camphor is unique in its ability to increase heart rate and reduce appetite. Research detailed as early as the 18th century shows that camphor can induce tachycardia, meaning that patients can sometimes experience an abnormally rapid heart rate, Interestingly, the increased heart rate tends to coincide with a decreased appetite, making this terpene similar to the cannabinoid THCV.