Hence why is best used for shallow wounds.
It is restricted for internal use in Australia.
The leaf contains allantoin, rosmarinic acid and varying degrees of pyrrolizidine alkaloids depending on species and time of harvest. It is the allantoin that has the healing properties.
Comfrey has also guarded against the deformation of scar tissue.
Generally an infusion (strong tea) of fresh or dried leaves is made and either to soak a part such as a sore finger or to dab on a cut with cotton. Crushed foliage can be applied externally, or a raw leaf rubbed on skin lesions such as rashes and sprains. Comfrey should not be applied to deep open wounds or broken skin.
Fresh comfrey is always best, though dried is better than nothing.
My husband injured himself playing footie and was told he would be 2 weeks out of the game. We poulticed his cracked ribs and he endured the discomfort he felt during the healing process and was playing footie again in three days.