Human skin color ranges from the darkest brown to the lightest hues. Differences in skin color among individuals is caused by variation in pigmentation, which is the result of genetics, exposure to the sun, disorders, or some combination thereof. Differences across populations evolved through natural selection or sexual selection, because of social norms and differences in environment, as well as regulations of the biochemical effects of ultraviolet radiation penetrating the skin.
Melanin is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes.
Melanocytes are melanin-producing neural crest-derived cells located in the bottom layer of the skin's epidermis, the middle layer of the eye, the inner ear, vaginal epithelium, meninges, bones, and heart found in many mammals and birds. Melanin is a dark pigment primarily responsible for skin color. Once synthesized, melanin is contained in special organelles called melanosomes which can be transported to nearby keratinocytes to induce pigmentation. Thus darker skin tones have more melanosomes present than lighter skin tones. Functionally, melanin serves as protection against UV radiation. Melanocytes also have a role in the immune system.
Acne, also known as acne vulgaris, is a long-term skin condition that occurs when dead skin cells and oil from the skin clog hair follicles. Typical features of the condition include blackheads or whiteheads, pimples, oily skin, and possible scarring. It primarily affects skin with a relatively high number of oil glands, including the face, upper part of the chest, and back. The resulting appearance can lead to lack of confidence, anxiety, reduced self-esteem, and, in extreme cases, depression or thoughts of suicide.
Laser hair removal is the process of hair removal by means of exposure to pulses of laser light that destroy the hair follicle. It had been performed experimentally for about twenty years before becoming commercially available in 1995–1996. One of the first published articles describing laser hair removal was authored by the group at Massachusetts General Hospital in 1998. Laser hair removal is widely practiced in clinics, and even in homes using devices designed and priced for consumer self-treatment. Many reviews of laser hair removal methods, safety, and efficacy have been published in the dermatology literature.
Hyperpigmentation is the darkening of an area of skin or nails caused by increased melanin.
Hypopigmentation is characterized specifically as an area of skin becoming lighter than the baseline skin color, but not completely devoid of pigment. This is not to be confused with depigmentation, which is characterized as the absence of all pigment. It is caused by melanocyte or melanin depletion, or a decrease in the amino acid tyrosine, which is used by melanocytes to make melanin. Some common genetic causes include mutations in the tyrosinase gene or OCA2 gene. As melanin pigments tend to be in the skin, eye, and hair, these are the commonly affected areas in those with hypopigmentation.
Melasma is a tan or dark skin discoloration. Melasma is thought to be caused by sun exposure, genetic predisposition, hormone changes, and skin irritation. Although it can affect anyone, it is particularly common in women, especially pregnant women and those who are taking oral or patch contraceptives or hormone replacement therapy medications.
Ochronosis is a syndrome caused by the accumulation of homogentisic acid in connective tissues. The condition was named after the yellowish (ocher-like) discoloration of the tissue seen on microscopic examination. Macroscopically, though, the affected tissues appear bluish-grey because of a light-scattering phenomenon known as the Tyndall effect. The condition is most often associated with alkaptonuria, but can occur from exogenous administration of phenol complexes such as hydroquinone. It was first described by Rudolf Virchow in 1865.
Liver spots are blemishes on the skin associated with aging and exposure to ultraviolet radiation from the sun. They range in color from light brown to red or black and are located in areas most often exposed to the sun, particularly the hands, face, shoulders, arms and forehead, and the scalp if bald.
Skin whitening, also known as skin lightening and skin bleaching, is the practice of using chemical substances in an attempt to lighten the skin or provide an even skin color by reducing the melanin concentration in the skin. Several chemicals have been shown to be effective in skin whitening, while some have proven to be toxic or have questionable safety profiles. This includes mercury compounds which may cause neurological problems and kidney problems.
β-Arbutin, also known by its International Nomenclature of Cosmetic Ingredients (INCI) name, arbutin, is a glycosylated derivative of hydroquinone. β-Arbutin is naturally present in the leaves and bark of a variety of plants, notably the bearberry plant, Arctostaphylos uva-ursi. Utilized as a biosynthetic active ingredient in topical treatments for skin lightening, β-arbutin is aimed at addressing hyperpigmentation issues. Its mechanism of action involves inhibiting the activity of tyrosinase, an essential enzyme for melanin synthesis in the human skin, thereby leading to a reduction in hyperpigmentation. It is important to distinguish β-arbutin from its structurally similar stereoisomer, α-arbutin, which exhibits similar effects in clinical applications.
Periorbital puffiness, also known as puffy eyes, or swelling around the eyes, is the appearance of swelling in the tissues around the eyes, called the orbits. It is almost exclusively caused by fluid buildup around the eyes, or periorbital edema. Minor puffiness usually detectable below the eyes only is often called eye bags. Such transient puffiness is distinct from the age related and gradual increase in the size of the fat pad lying below the lower eyelids which can also be colloquially referred to as eye bags.
A Dennie–Morgan fold, also known as a Dennie–Morgan line or an infraorbital fold, is a fold or line in the skin below the lower eyelid. It can simply be an ethnic/genetic trait, but was found in one study to occur in 25% of patients with atopic dermatitis. The presence of Dennie–Morgan folds can be used as a diagnostic marker for allergy, with a sensitivity of 78% and specificity of 76% for atopic dermatitis according to one study, although another study found them to be of diagnostic significance in atopic dermatitis. The condition was described by Charles Clayton Dennie and David B. Morgan in 1948.
Periorbital hyperpigmentation, also known as hereditary dark circles, is characterized by darker skin around the eyes caused by the presence of additional melanin. It is an extremely common hereditary human characteristic and is frequently found on individuals with dark skin. Periorbital hyperpigmentation is most prevalent within the 16–25 age group.
Postinflammatory hypopigmentation is a cutaneous condition characterized by decreased pigment in the skin following inflammation of the skin.
Oral pigmentation is asymptomatic and does not usually cause any alteration to the texture or thickness of the affected area. The colour can be uniform or speckled and can appear solitary or as multiple lesions. Depending on the site, depth, and quantity of pigment, the appearance can vary considerably.
Glyceryl octyl ascorbic acid (GO-VC) is an amphipathic derivative of vitamin C consisting of two ether linkages: a 1-octyl at position 2 and a glycerin at position 3. The chemical name is 2-glyceryl-3-octyl ascorbic acid. The isomer in which these two groups are swapped is also known.
Postinflammatory hyperpigmentation (PIH) is a skin condition characterized by the darkening of the skin (hyperpigmentation) following an inflammatory injury, such as acne, dermatitis, infectious disease, or trauma. Less frequently, it may occur as a complication of a medical procedure performed on the skin. It is a common cause of skin discoloration and can affect individuals of all skin types.
α-Arbutin, is a glycosylated hydroquinone, and an anomer of the naturally occurring arbutin. α-Arbutin is used in the cosmetic and pharmaceutical industries for its skin lightening effects, treatment of hyperpigmentation, and as a safer alternative to hydroquinone.
