It has been discovered that granulocyte macrophage colony stimulating factor (“GM-CSF”) promotes migration of activated (but not differentiating) keratinocytes to wound sites. It was also discovered that GM-CSF increases the quantity and improves the quality of collagen. This growth factor specifically increases migration of keratinocytes of the “wound” phenotype but does not have significant effects upon differentiated keratinocytes. Examples demonstrate reversal of skin impairment in multiple animal models of diabetic skin imparment when provided in an effective amount over an effective time period. The examples also demonstrate the efficacy of the formulations in cosmetic applications. A preferred formulation is a sustained release formulation that delivers sufficient growth factor to the skin and the underlying tissue thereof to increase the rate of keratinocyte migration, as well as collagen deposition and fibroblast proliferation, in the skin to promote rejuvenation of skin injuries resistant to repair due to underlying disease, such as diabetes, or aging.