Collagen is the primary structural protein in the dermal extracellular matrix. Its fibers
provide tensile strength and mechanical support but have low elasticity. Aging and UV
radiation reduce fibroblast activity and collagen biosynthesis while altering collagen
structure and organization as the dermis thins. Consequently, the skin loses elasticity and
firmness, resulting in wrinkles and sagging. Collagen of animal and biotechnological
origin is therefore increasingly used in cosmetic and nutricosmetic products for mature and
photoaged skin. Because native collagen cannot penetrate the stratum corneum owing to its
high molecular weight, dermal products generally contain hydrolyzed collagen or lower-
molecular-weight peptides, which also have better technological properties and are easier
to incorporate into formulations. This thesis reviewed recent clinical studies on the effects
of dermal and oral collagen administration on skin hydration and barrier function,
biomechanical properties, and wrinkle appearance and severity. The results indicate that
both administration routes may improve skin hydration, barrier function, biomechanical
properties, and skin texture. Six studies of dermal products containing primarily
hydrolyzed collagen reported improved hydration, reduced transepidermal water loss
(TEWL) and roughness, and less pronounced wrinkles. However, because the effects
depend on product composition and formulation technology, evidence for the standalone
effects of dermal collagen remains limited, and further methodologically robust studies are
needed. Oral administration, particularly of hydrolyzed collagen and collagen peptides,
was adequately investigated in five randomized, double-blind studies, four of which were
placebo-controlled. Several weeks of use were associated with improved skin hydration
and elasticity, reduced wrinkle appearance, and increased dermal collagen density.
Nevertheless, these effects cannot always be attributed exclusively to collagen, as they are
also influenced by peptide properties and formulation composition. A review of collagen-
containing products revealed a wide variety, with cosmetic products mainly available in
drugstores and nutricosmetics in online pharmacies. Most selected products contained
hydrolyzed collagen. Dermal products were predominantly face creams, serums, and
masks, with marketing claims focused on moisturizing, reducing wrinkle appearance, and
improving skin firmness.
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