Extract for which there is little research showing it to have any benefit for skin. What studies do exist were performed in vitro, and indicate that it may have skin-soothing properties. However, yarrow also has properties that may cause skin sensitivity and photosensitivity.
References for this information:
Healthnotes Review of Complementary and Integrative Medicine, www.healthwell.com/healthnotes/herb
Planta Medica, 1991, volume 57, pages 444–446, and 1994, volume 60, pages 37–40