Numerous placebo-controlled human studies have demonstrated that oral intake of collagen peptides improves the condition of skin and joints and promotes healing of pressure ulcers. However, it was initially thought that collagen peptides taken orally would be broken down into amino acids, so no special effects were expected from oral intake. However, it has been revealed that high levels of food-derived collagen peptides (> 10 μM) circulate in the peripheral blood of humans for several hours after ingestion of collagen peptides (10–22 g). The main component is Pro-Hyp. Pro-Hyp is also produced by the degradation of endogenous collagen at wound sites. Pro-Hyp promotes the proliferation of fibroblasts expressing the mesenchymal stem cell marker (p75NTR), which plays an important role in granulation tissue formation in wound healing, but does not act on p75NTR-negative fibroblasts present in normal tissues. These results suggest that food-derived Pro-Hyp promotes the repair of damaged tissues through the proliferation of fibroblasts differentiated from mesenchymal stem cells, which may be one of the factors contributing to the effects of orally ingested collagen peptides.