WebMD reveals that Vicks VapoRub can be dangerous when too much is applied or if it is applied to broken or injured skin or ingested by mouth. Camphor, the active ingredient in Vicks VapoRub, can lead to severe side effects, including death, when used inappropriately.
When applied to broken skin or ingested by mouth, the camphor in Vicks VapoRub is quickly and easily absorbed, leading to toxic levels in the body, states WebMD. Symptoms of toxicity include burning of the mouth and throat, nausea and vomiting. WebMD advises that it is likely safe to use products containing less than 11 percent camphor when applied to the skin in low concentrations.