188
J. Cosmet. Sci., 74.3, 188–199 (May/June 2023)
*Address all correspondence to Galina Yarova, galina.yarova@unilever.com
In Vivo Elongation of Topically Applied Fatty Acids From a
Range of Different Topical Skincare Formulations
GALINA YAROVA, WILLIAM F. LATHROP, ANDREW E. MAYES, STACY HAWKINS,
BRIAN DOBKOWSKI, BIVASH R. DASGUPTA AND JOHN S. BAJOR
Department of Human Biology, Unilever U.S. Research &Development, Trumbull, Connecticut, USA
(G.Y., W.L. J.B.)
Unilever U.S. Research &Development, Clinicals, Trumbull, Connecticut, USA (S.H.)
Unilever U.S. Research &Development, Product Development, Trumbull, Connecticut, USA (B.D., B.D.)
Department of Human Biology, Unilever U.K. Research &Development, Colworth Science Park,
Sharnbrook, Bedford, United Kingdom (A.M.)
Accepted for publication August 05, 2023.
Synopsis
The lipid matrix of the stratum corneum (SC) is essential to skin barrier function, and detrimental structural
changes may occur in response to human behaviour, disease, and external factors. The application of topical
formulations is a common approach to repairing the SC and has been investigated ex vivo and in vitro. We
aim to demonstrate the first clinical evidence of deuterated palmitic acid (d31-PA) deposition from topical
formulations into the SC of human skin in vivo and its conversion into longer-chain free fatty acids (FFAs) and
ceramides. Healthy female participants aged 30 to 50 years old participated in two separate product application
studies. Participants were randomized to an application of a leave-on lotion or a syndet bar containing d31-PA
in the first study, with the second study having an option of a body wash containing different levels of d31-PA.
Skin tapes and solvent extracts were collected at baseline and Day 28. Lipid composition and the presence
of deuterated sphingosine were analyzed by liquid chromatography tandem mass spectrometry (LC/MS/MS).
After four weeks, d31-PA was sufficiently delivered into the SC by all topical formulations. LC/MS/MS data
show that FFAs are elongated up to C26:0 and used in the formation of ceramides and free sphingosine. These
data provide the first in vivo evidence that FFAs deposited from a range of different topical formulations are
elongated in the SC and provide the building blocks for ceramide synthesis. Together, the evidence shows
that commercially available topical formulations can nourish the skin which may contribute to maintaining
a healthy skin barrier.
INTRODUCTION
The skin is the largest organ of the human body, with a surface area of 1.5 m2 in adults,
and acts as a barrier between the body’s interior and external environment.1 The uppermost
epidermal layer of the skin, the stratum corneum (SC), comprises corneocyte layers embedded
in a lipid matrix, which acts as the main pathway for the diffusion of substances through
J. Cosmet. Sci., 74.3, 188–199 (May/June 2023)
*Address all correspondence to Galina Yarova, galina.yarova@unilever.com
In Vivo Elongation of Topically Applied Fatty Acids From a
Range of Different Topical Skincare Formulations
GALINA YAROVA, WILLIAM F. LATHROP, ANDREW E. MAYES, STACY HAWKINS,
BRIAN DOBKOWSKI, BIVASH R. DASGUPTA AND JOHN S. BAJOR
Department of Human Biology, Unilever U.S. Research &Development, Trumbull, Connecticut, USA
(G.Y., W.L. J.B.)
Unilever U.S. Research &Development, Clinicals, Trumbull, Connecticut, USA (S.H.)
Unilever U.S. Research &Development, Product Development, Trumbull, Connecticut, USA (B.D., B.D.)
Department of Human Biology, Unilever U.K. Research &Development, Colworth Science Park,
Sharnbrook, Bedford, United Kingdom (A.M.)
Accepted for publication August 05, 2023.
Synopsis
The lipid matrix of the stratum corneum (SC) is essential to skin barrier function, and detrimental structural
changes may occur in response to human behaviour, disease, and external factors. The application of topical
formulations is a common approach to repairing the SC and has been investigated ex vivo and in vitro. We
aim to demonstrate the first clinical evidence of deuterated palmitic acid (d31-PA) deposition from topical
formulations into the SC of human skin in vivo and its conversion into longer-chain free fatty acids (FFAs) and
ceramides. Healthy female participants aged 30 to 50 years old participated in two separate product application
studies. Participants were randomized to an application of a leave-on lotion or a syndet bar containing d31-PA
in the first study, with the second study having an option of a body wash containing different levels of d31-PA.
Skin tapes and solvent extracts were collected at baseline and Day 28. Lipid composition and the presence
of deuterated sphingosine were analyzed by liquid chromatography tandem mass spectrometry (LC/MS/MS).
After four weeks, d31-PA was sufficiently delivered into the SC by all topical formulations. LC/MS/MS data
show that FFAs are elongated up to C26:0 and used in the formation of ceramides and free sphingosine. These
data provide the first in vivo evidence that FFAs deposited from a range of different topical formulations are
elongated in the SC and provide the building blocks for ceramide synthesis. Together, the evidence shows
that commercially available topical formulations can nourish the skin which may contribute to maintaining
a healthy skin barrier.
INTRODUCTION
The skin is the largest organ of the human body, with a surface area of 1.5 m2 in adults,
and acts as a barrier between the body’s interior and external environment.1 The uppermost
epidermal layer of the skin, the stratum corneum (SC), comprises corneocyte layers embedded
in a lipid matrix, which acts as the main pathway for the diffusion of substances through
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