Cosmeceuticals Part 1

Introduction

Cosmeceuticals
represent a marriage between cosmetics and pharmaceuticals. Like cosmetics,
cosmeceuticals are topically applied, but they contain ingredients that
influence the biological function of the skin. Cosmeceuticals improve
appearance, but they do so by delivering nutrients necessary for healthy skin.
Cosmeceuticals are the fastest-growing segment of the natural personal care
industry. Consumers are always interested in maintaining a youthful appearance,
and as the global population's median age increases, this market is
increasingly expanding.

Cosmeceuticals
are not subject to review by the Food and Drug Administration (FDA), and the
term cosmeceutical is not recognized by the Federal Food, Drug, and Cosmetic
Act. Although cosmetics and cosmeceuticals are tested for safety, testing to
determine whether beneficial ingredients actually live up to a manufacturer's
claims is not mandatory. In general, vitamins, herbs, various oils, and
botanical extracts may be used in cosmeceuticals, but the manufacturer may not
claim that these products penetrate beyond the skin's surface layers or that
they have druglike or therapeutic effects. For cosmetic labels, no division
between active ingredients and other ingredients is required; they are all
listed together.

Moisturizers

The
cutaneous permeability barrier is localized in the stratum corneum interstices,
and it is mediated by the lamellar bilayers enriched in cholesterol, free fatty
acids, and ceramides. Formulations containing skin-identical lipids have been
suggested to facilitate a cascade of physiologic events in keratinocytes,
normalizing damaged skin. When applied to the skin for an extended period,
water can cause the excretion of cytokines. These proinflammatory molecules
induce edema, vasodilation, and frank inflammation; therefore, water alone may
alter both the structure and the function of the skin under some conditions. By
the same token, moisturizers that make the stratum corneum softer and more
pliant by increasing its hydration could be considered cosmeceuticals.

Retinoids

Retinoids
are possibly the most prevalent cosmeceuticals in the market. Retinoids are
vitamin A derivatives present in all living organisms either as preformed
vitamin A or as carotenoids. Vitamin A (retinol) is the prototype of all other
retinoids and is necessary for proper growth, bone development, and integrity
of mucosal and epithelial surfaces. In vitamin A deficiency, the eyes and the
skin are severely affected. The conjunctiva and the cornea develop metaplasia
and keratinization, leading to night blindness. The skin develops follicular
hyperkeratosis or phrynoderma. The hyperkeratotic follicular papules are
usually clustered around bony prominences, such as the elbows and the knees,
but in severe deficiency, the papules can be found throughout the entire skin
surface.

Early civilizations recognized the benefits of vitamin A in treating and healing
night blindness with diets rich in liver. In the 1930s, the clinical
manifestations of vitamin A deficiency were recognized, and the idea to use
vitamin A in the treatment of skin diseases was initiated. The advent of
synthetic analogs of vitamin A in the 1970s brought new interest into their
biological activity, especially on the skin. Since then, vitamin A and its
derivatives have been useful in the treatment of many skin disorders, including
ichthyosis, acne, and psoriasis. A great amount of research has concentrated on
its use as an antiaging compound as well as its use for other cutaneous
disorders; therefore, today, vitamin A is recognized as comprising a magnitude
of biological effects far beyond those on the cornea.

VitaminA and its derivatives have 2 main functions: they act as antioxidants, and they
activate specific genes and proteins. As antioxidants, they protect cells from
oxidative damage by 3 different mechanisms: (1) scavenging peroxyl radicals,
(2) quenching singlet oxygen, and (3) triplet-state sensitizers. Vitamin A also
exerts a hormonelike effect on the skin, activating specific genes through
nuclear receptors. The receptors bind to target sequences called hormone
response elements on DNA and activate gene transcription. Retinoic acid
receptors (RARs) bind all-trans retinoic acid, and retinoic X receptors
(RXRs) bind 9-cis retinoic acid. Vitamin A and its derivatives inhibit
lipid peroxidation; increase levels of alpha-tocopherol (vitamin E); and
activate growth factors, oncogenes, keratins, and transglutaminases.

Histologically,vitamin A and its derivatives induce epidermal thickening, increase mitoses,
differentiate keratinocytes, and reduce the number of sebocytes. The dermis
shows increased amounts of glycosaminoglycans (GAGs) and anchoring fibrils.
Structural changes underlying the cosmetic benefits include correction of
epidermal atrophy, deposition of new collagen, generation of new vessels, and
enhancement of mitogenesis. This enhanced mitogenesis promotes the shedding of
melanin-laden keratinocytes, resulting in bleaching and subsequent
depigmentation. The ability of topical tretinoin to improve the appearance of
aged and photo-damaged skin by reducing wrinkles, decreasing laxity, bleaching
hyperpigmented spots, and bringing about a smoother surface have been well
studied and documented. Further remedial qualities of retinoids remain to be
elucidated.