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Tripeptide-29
Glycyl-prolyl-hydroxyproline, the collagen tripeptide behind the INCI name: how much of it reaches the blood, what it does in cells and mice, and why the human trials do not test it alone
Tripeptide-29 is the cosmetic ingredient name for glycyl-prolyl-hydroxyproline (Gly-Pro-Hyp), the three-amino-acid unit that repeats through collagen. It is a component of collagen hydrolysates and of 'collagen tripeptide' supplements. Studies in people show that Gly-Pro-Hyp appears in the blood after they drink collagen preparations rich in tripeptides, and studies in rats measured how much of the pure tripeptide is absorbed. In cells and mice it protected skin cells and countered sun damage. No human trial has given Gly-Pro-Hyp on its own, so its effects in people are unknown.
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What is it?
Collagen is built from a repeating pattern of three amino acids, glycine followed by two others, and glycine-proline-hydroxyproline is one of those triplets; a 2026 study calls it the main component of collagen tripeptide preparations. As a free tripeptide it is listed in cosmetics under the INCI name tripeptide-29, and it is one of the main pieces in collagen hydrolysates, especially products made with enzymes that cut collagen into tripeptides and sold as 'collagen tripeptide'.
Most of the research asks whether it survives digestion. In rats given pure Gly-Pro-Hyp, about 4.4% of an oral dose reached the bloodstream intact, less than its breakdown product Pro-Hyp. In pig intestinal membranes the tripeptide was trimmed to Pro-Hyp before crossing, while in a layer of cultured intestinal cells some crossed intact. In people who drank tripeptide-rich collagen preparations, Gly-Pro-Hyp rose in the blood and appeared in the urine, and the amount tracked how much of it the drink contained. In mice, Gly-Pro-Hyp and Pro-Hyp reached the skin.
What it does once there is known only from the laboratory and animals. It protected liver cells from damage by a reactive sugar product and blocked the formation of toxic glycation products more strongly than its breakdown pieces; it preserved collagen and elastin gene activity in skin fibroblasts under oxidative stress; and in mice exposed to ultraviolet light, Gly-Pro-Hyp itself countered photoaging about as well as a tripeptide-rich hydrolysate. It also binds iron, which has been proposed as a way to help iron absorption.
The human trials of skin and inflammation gave collagen tripeptide products, which are mixtures of many Gly-X-Y tripeptides, not tripeptide-29 alone, so they cannot show what Gly-Pro-Hyp itself does. They are listed under References. That is why this entry is a mid-tier page: the literature on the molecule itself is mostly about absorption, with a handful of cell and mouse studies and no controlled human study of the tripeptide on its own.
At a Glance
Every value in this table is printed from the Grey Peptides dataset, the same record the compound explorer and comparison tool read, so the three can never disagree.
Published Research
These studies were read from their PubMed abstracts on October 29, 2026. Three measured Gly-Pro-Hyp in the blood of people after collagen preparations; the rest are rat absorption studies, membrane and cell-layer transport studies, cell experiments and a mouse photoaging study. Every card tested or measured Gly-Pro-Hyp itself. Two human trials of collagen tripeptide mixtures are listed under References.
Gly-Pro-Hyp reaches the blood in people and the skin in mice
After people drank a collagen hydrolysate high in tripeptides, 17 collagen-derived peptides rose briefly in their plasma, with Gly-Pro-Hyp especially prominent. In mice the same happened in plasma and skin, where Pro-Hyp predominated; giving pure Gly-Pro-Hyp showed that skin Pro-Hyp came from breakdown of the tripeptide.
Absorption and urine excretion in people
In people given a tripeptide fraction of collagen, a preparation about half tripeptides, or an ordinary collagen peptide, plasma Gly-Pro-Hyp and Pro-Hyp rose only with the tripeptide products and in proportion to the Gly-Pro-Hyp ingested. Both also appeared in the urine in peptide form, again in proportion to the amount taken.
One collagen product raised Gly-Pro-Hyp; the tripeptide helped skin cells
Comparing plasma peptides after four collagen preparations, only Gly-Pro-Hyp rose significantly more after one tripeptide-rich product than after general collagen peptides or collagen. In dermal fibroblasts under hydrogen peroxide stress, Gly-Pro-Hyp itself prevented the fall in collagen I, elastin and fibronectin gene activity.
Pharmacokinetics of the pure tripeptide in rats
Given to rats by vein or stomach tube, Gly-Pro-Hyp had an absolute oral bioavailability of about 4.4%, against 19.3% for Pro-Hyp, reflecting more first-pass breakdown; absorption was slow, plasma levels showed a double peak, and about 6% of an intravenous dose appeared unchanged in urine.
Stable in gut fluid, crosses an intestinal cell layer
Gly-Pro-Hyp and Pro-Hyp stayed intact for two hours in gastrointestinal fluid and rat plasma, Gly-Pro-Hyp crossed a layer of intestinal cells, and rats given a fish-scale collagen tripeptide preparation had higher plasma levels of both than rats given a high-molecular-weight collagen peptide.
Trimmed to Pro-Hyp at the gut membrane
In pig intestinal brush-border membrane vesicles, Gly-Pro-Hyp was split into glycine and Pro-Hyp by a membrane enzyme, and Pro-Hyp then entered through the PEPT1 transporter; the intact tripeptide did not cross in this model.
Protects cells from glycation damage
In liver cells exposed to glyceraldehyde, only Gly-Pro-Hyp, not its constituent amino acids or smaller peptides, reduced cell death and IL-8 expression. It inhibited the formation of toxic advanced glycation end-products and protein cross-linking more strongly than its metabolites and mopped up glyceraldehyde within the first hour.
Counters photoaging in UV-exposed mice
In mice exposed to ultraviolet light, a collagen hydrolysate rich in Gly-Pro-X tripeptides raised blood Gly-Pro-Hyp about 65-fold over a low-tripeptide hydrolysate and better protected skin collagen, hyaluronic acid, elasticity and thickness. Gly-Pro-Hyp given on its own showed comparable anti-photoaging activity.
Binds iron more strongly than its pieces
Potentiometric measurements showed Gly-Pro-Hyp forms more stable complexes with ferric iron than Pro-Hyp or glycine at body temperature and nearby temperatures, which the authors propose could make it a promoter of iron absorption.
Side Effects & Contraindications
Reported Side Effects
No safety study of Gly-Pro-Hyp itself was found.
Contraindications & Cautions
A cosmetic and supplement ingredient with no drug label. These cautions follow from the evidence.
Legal Status
Tripeptide-29 is a cosmetic and supplement ingredient, not a medicine.
Frequently Asked Questions
?What is tripeptide-29?
The INCI (cosmetic ingredient) name for glycyl-prolyl-hydroxyproline, Gly-Pro-Hyp, the repeating three-amino-acid unit of collagen.
?Is it absorbed when swallowed?
Partly. In rats about 4.4% of a dose of the pure tripeptide reached the blood intact, and people who drank tripeptide-rich collagen preparations had more Gly-Pro-Hyp in their blood and urine.
?Does tripeptide-29 improve skin?
In skin cells under stress and in UV-exposed mice it helped preserve collagen and counter photoaging. The human skin trials tested collagen tripeptide mixtures, not tripeptide-29 alone, so its own effect in people is unknown.
?Is it the same as collagen tripeptide supplements?
No. 'Collagen tripeptide' products are mixtures of many Gly-X-Y tripeptides in which Gly-Pro-Hyp is one component. Tripeptide-29 is the single tripeptide.
?Why is this a shorter entry?
Because the studies of Gly-Pro-Hyp itself are mostly about absorption, with a few cell and mouse experiments; no controlled human study has tested it on its own.
References
- [other] PubChem CID 11778669, Glycyl-prolyl-hydroxyproline: formula C12H19N3O5, molecular weight 285.30. Read October 28, 2026. https://pubchem.ncbi.nlm.nih.gov/compound/11778669
- [clinical-trial] Yazaki M, et al. "Oral Ingestion of Collagen Hydrolysate Leads to the Transportation of Highly Concentrated Gly-Pro-Hyp and Its Hydrolyzed Form of Pro-Hyp into the Bloodstream and Skin." J Agric Food Chem, 2017;65(11):2315-2322. PMID: 28244315.
- [clinical-trial] Yamamoto S, et al. "Absorption and Urinary Excretion of Peptides after Collagen Tripeptide Ingestion in Humans." Biol Pharm Bull, 2016;39(3):428-34. PMID: 26934933.
- [clinical-trial] Chae M, et al. "Oral Ingestion of AP Collagen Peptide Leads to Systemic Absorption of Gly-Pro-Hyp, Alleviating H(2)O(2)-Induced Dermal Fibroblast Aging." J Med Food, 2023;26(5):299-306. PMID: 37074675.
- [pubmed] Won J, et al. "Pharmacokinetics of collagen dipeptides (Gly-Pro and Pro-Hyp) and tripeptides (Gly-Pro-Hyp) in rats." J Food Sci, 2024;89(1):701-709. PMID: 38051020.
- [pubmed] Sontakke SB, et al. "Orally Available Collagen Tripeptide: Enzymatic Stability, Intestinal Permeability, and Absorption of Gly-Pro-Hyp and Pro-Hyp." J Agric Food Chem, 2016;64(38):7127-33. PMID: 27573716.
- [pubmed] Aito-Inoue M, et al. "Transport of a tripeptide, Gly-Pro-Hyp, across the porcine intestinal brush-border membrane." J Pept Sci, 2007;13(7):468-74. PMID: 17554807.
- [pubmed] Yamamoto S, et al. "The Glycine-Proline-Hydroxyproline Tripeptide Reduces Cell Death Caused by Glycative Stress." Protein Pept Lett, 2026;33(2):454-464. PMID: 42116558.
- [pubmed] Yang D, et al. "Effects of collagen hydrolysates on UV-induced photoaging mice: Gly-Pro-Hyp as a potent anti-photoaging peptide." Food Funct, 2024;15(6):3008-3022. PMID: 38411396.
- [pubmed] Zhi M, et al. "Complex formation constant of ferric ion with Gly, Pro-Hyp and Gly-Pro-Hyp." RSC Adv, 2018;8(48):27157-27162. PMID: 35539970.
- [pubmed] Hakuta A, et al. "Anti-inflammatory effect of collagen tripeptide in atopic dermatitis." J Dermatol Sci, 2017;88(3):357-364. PMID: 29017796.
- [pubmed] Lee YI, et al. "Effect of a Topical Collagen Tripeptide on Antiaging and Inhibition of Glycation of the Skin: A Pilot Study." Int J Mol Sci, 2022;23(3). PMID: 35163025.
Sources & Citations
Every study on this page was read from its PubMed record on October 29, 2026. Identity comes from PubChem (CID 11778669); status from Drugs@FDA and the EMA medicines list, read October 28, 2026. PubMed held 16 records with Gly-Pro-Hyp in the title and none naming tripeptide-29; ClinicalTrials.gov, Drugs@FDA and the EMA list returned none (October 28, 2026). Grey Peptides sells nothing and links to no vendor.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Consult a licensed healthcare provider before making health decisions.