The Essential Herbal, Alicia Grosso provides a glorious bouquet of ways to use yarrow for the relief of summer's irritations. Here's one, excerpted from her article - simple to make, and very versatile.
Yarrow Bath Tea and Compress
Dry lavender flowers
Dry rose petals
Dry milk powder
Light muslin square, reusable muslin bag or heat-seal tea bag
Make a mixture of dried botanicals. Three parts yarrow, one part lavender, one part rose petals, one part dry milk. Store a bulk amount in a dry jar with an airtight lid. Fill bags as needed and drop one into a warm bath. Alternatively, use the saturated bag as a small compress for sunburn. Gently swab tender areas.