British scientists believe they may have discovered how the popular herbal remedy arnica works.
Arnica is often used to treat muscle pain or strains
Researchers from the Bradford School of Pharmacy say it contains powerful anti-inflammatory agents which can be absorbed into the skin.
Speaking at the British Pharmaceutical Conference in Harrogate, they suggested it may protect damaged blood vessels.
Arnica is used in creams to treat a wide variety of ailments, including bruising, muscle ache and sprains.
Professor Adrian Williams and colleagues tested a product containing arnica in their laboratory.
They examined it to see if it could pass through human skin.
Initially, their tests showed that it could not be absorbed by the skin.
However, after 12 hours they discovered that two components had permeated the skin.
Further tests found that these were anti-inflammatory agents called sesquiterpene lactones, which are found in arnica.
The scientists believe that this may explain why arnica may prevent bruising.
Professor Williams said: "This is good evidence - but not yet proof - that these are the vasoactive agents that prevent bruising."
But he added: "The curious aspect is that we did not see permeation in the first 12 hours.
"To prevent bruising the agents will have to act quickly to stop capillary bleeding.
"Active agents are presumably getting through the skin but in
such small quantities that it takes 12 hours for the amount to be detectable.
"For such low concentrations to be effective, the active agents must be very potent."
At present, arnica preparations are not standardised which means some may contain more of these active ingredients than others.
This may explain why some people claim it doesn't work while others insist it does.
Professor Williams suggested that one approach may be to purify just these active ingredients.
However, because they are present in such small concentrations this is unlikely to be commercially viable.
As a result, Professor Williams and his team are now looking at ways of manufacturing these agents.