Background　In recent years, attention to nails has been increasing with nail cosmetics and the like. It has been known that continuous oral ingestion of gelatin is effective for keeping nails healthy since the 1950's, but no similar function has been reported in collagen peptide.
Objectives　We investigated whether continuous ingestion of porcine skin derived collagen peptide having the function of improving the horny water content of human skin improves moisture content of human nails and inhibits hardening.
Methods　20 healthy adult females（31 to 51 years old, average age 41 years old）who have troubles with such as nail fragile, thinly peeled off, were randomly divided into two groups of control（dextrin）or porcine skin derivered collagen peptide. After ingestion 5 g/day for 12 weeks, they were measured the moisture content, moisture transpiration amount, hardness, sphingosine and ceramide content of the lunula of right thumb nail plate.
Results　Oral ingestion of porcine skin derived collagen peptide increased the moisture content of nail and suppressed the increase of TEWL of nail compared with control. It was also shown that the hardness of the nail was reduced, indicating that the nail's water retention and suppleness are improved. As a result of measuring the amount of intercellular lipids such as sphingosine and ceramide in the nail, the amount of sphingosine and ceramide in the nail increased by ingestion of porcine skin derived collagen peptide.
Conclusions　From these results, it was revealed that oral ingestion of porcine skin derived collagen peptide prevents drying by keeping the nail's water retentivity by increasing the inter‐cellular lipids in the nail, and improves supple nail flexibility.