Dang Gui Si Ni Tang is a classical warming and blood-nourishing formula traditionally used for cold hands and feet due to blood deficiency with cold obstructing the channels. By combining warming herbs like Gui Zhi and Gan Jiang with blood-nourishing Dang Gui and Bai Shao, this formula restores circulation to the extremities while harmonizing the nutritive and protective Qi. In modern terms, it supports microvascular flow, reduces cold-induced vasospasm, and alleviates pain and numbness from impaired peripheral circulation. Within the context of Lingering Pathogenic Illness, Dang Gui Si Ni Tang may be particularly useful for conditions such as “Covid toes” or chilblain-like lesions, where immune dysregulation and microvascular inflammation are worsened by cold exposure. By both warming and nourishing, it addresses the root deficiency while ensuring blood can reach the periphery, offering relief from cold extremities, swelling, and discomfort.