Oh my gosh, I was curious and looked it up after I saw your comment and found all kinds of stuff about this. Here is a portion of what I learned:
The plant also has a long history as a powerful 'healing herb' used topically for wounds, cuts and abrasions. The genus name Achillea is derived from mythical Greek character, Achilles, who reportedly carried it with his army to treat battle wounds. This medicinal action is also reflected in some of the common names mentioned below, such as staunchweed and soldier's woundwort. Yarrow, Achillea millefolium and its North American varieties, was used in traditional Native American herbal medicine by tribes across the continent. The Navajo considered it to be a "life medicine", chewed it for toothaches, and poured an infusion into ears for earaches. The Miwok in California used the plant as an analgesic and head cold remedy.
Several tribes of the Plains Indians used common yarrow. The Pawnee used the stalk for pain relief. The Chippewa used the leaves for headaches by inhaling it in a steam. They also chewed the roots and applied the saliva to their appendages as a stimulant. The Cherokee drank a tea of common yarrow to reduce fever and aid in restful sleep.
Among the Zuni people use the occidentalis variety medicinally. The blossoms and root are chewed, and the juice applied before fire-walking or fire-eating. A poultice of the pulverized plant is mixed with water and applied to burns.
Isnt that amazing? Thanks for asking the question or I never would have been curious enough to check into it :) And I Just thought the flowers were pretty, I didn't know they could be so useful too!!! Lol