“Researchers from the Bradford School of Pharmacy say it contains powerful anti-inflammatory agents which can be absorbed into the skin.”
Two components of arnica are absorbed into the skin which can only be detected after 12 hours of exposure. Both are anti-inflammatories called sesquiterpene lactones.
To prevent bruising, arnica must be working quickly to stop capillary bleeding but amounts are so small that they are only detectable after 12 hours have passed.
“For such low concentrations to be effective, the active agents must be very potent.”