Piebaldism is a rare autosomal dominant disorder of melanocyte development. Common characteristics include a congenital white forelock, scattered normal pigmented and hypopigmented macules and a triangular shaped depigmented patch on the forehead. There is nevertheless great variation in the degree and pattern of presentation, even within affected families. In some cases, piebaldism occurs together with severe developmental problems, as in Waardenburg syndrome and Hirschsprung's disease. It has been documented to occur in all races; early photographers captured many images of African piebalds used as a form of amusement, and George Catlin is believed to have painted several portraits of Native Americans of the Mandan tribe who were affected by piebaldism. Piebaldism is found in nearly every species of mammal. It is very common in mice, rabbits, dogs, sheep, deer, cattle and horses—where selective breeding has increased the incidence of the mutation-, but occurs among chimpanzees and other primates only as rarely as among humans. Piebaldism is completely unrelated to acquired or infectious conditions such as vitiligo or poliosis.

"Pie" is a word for multi-colored and "bald" is related to a root word for "skin." Although piebaldism may visually appear to be partial albinism, it is a fundamentally different condition. The vision problems associated with albinism are not usually present as eye pigmentation is normal. Piebaldism differs from albinism in that the affected cells maintain the ability to produce pigment but have that specific function turned off. In albinism the cells lack the ability to produce pigment altogether. Human piebaldism has been observed to be associated with a very wide range and varying degrees of endocrine disorders, and is occasionally found together with heterochromia of the irises, congenital deafness, or incomplete gastrointestinal tract development, possibly all with the common cause of premature cutting off of human fetal growth hormone during gestation. Piebaldism is a kind of neurocristopathy, involving defects of various neural crest cell lineages that include melanocytes, but also involving many other tissues derived from the neural crest. Oncogenic factors, including mistranscription, are hypothesized to be related to the degree of phenotypic variation among affected individuals.

In humans, there are two principal types of albinism: oculocutaneous, affecting the eyes, skin and hair, and ocular affecting the eyes only.

There are different types of oculocutaneous albinism depending on which gene has undergone mutation. With some there is no pigment at all. The other end of the spectrum of albinism is "a form of albinism called rufous oculocutaneous albinism, which usually affects dark-skinned people".

According to the National Organization for Albinism and Hypopigmentation, "With ocular albinism, the color of the iris of the eye may vary from blue to green or even brown, and sometimes darkens with age. However, when an eye doctor examines the eye by shining a light from the side of the eye, the light shines back through the iris since very little pigment is present."

Because individuals with albinism have skin that entirely lacks the dark pigment melanin, which helps protect the skin from the sun's ultraviolet radiation, their skin can burn more easily from overexposure.

The human eye normally produces enough pigment to color the iris blue, green or brown and lend opacity to the eye. In photographs, those with albinism are more likely to demonstrate "red eye", due to the red of retina being visible through the iris. Lack of pigment in the eyes also results in problems with vision, both related and unrelated to photosensitivity.

Those afflicted with albinism are generally as healthy as the rest of the population (but see related disorders below), with growth and development occurring as normal, and albinism by itself does not cause mortality, although the lack of pigment blocking ultraviolet radiation increases the risk of melanomas (skin cancers) and other problems.

Development of the optical system is highly dependent on the presence of melanin. For this reason, the reduction or absence of this pigment in people with albinism may lead to:

- Misrouting of the retinogeniculate projections, resulting in abnormal decussation (crossing) of optic nerve fibres

- Photophobia and decreased visual acuity due to light scattering within the eye (ocular straylight) Photophobia is specifically when light enters the eye, unrestricted—with full force. It is painful and causes extreme sensitivity to light.

- Reduced visual acuity due to foveal hypoplasia and possibly light-induced retinal damage.

Eye conditions common in albinism include:

- Nystagmus, irregular rapid movement of the eyes back and forth, or in circular motion.

- Amblyopia, decrease in acuity of one or both eyes due to poor transmission to the brain, often due to other conditions such as strabismus.

- Optic nerve hypoplasia, underdevelopment of the optic nerve.

The improper development of the retinal pigment epithelium (RPE), which in normal eyes absorbs most of the reflected sunlight, further increases glare due to light scattering within the eye. The resulting sensitivity (photophobia) generally leads to discomfort in bright light, but this can be reduced by the use of sunglasses or brimmed hats.

Leucism (; or ) is a condition in which there is partial loss of pigmentation in an animal resulting in white, pale, or patchy coloration of the skin, hair, feathers, scales or cuticle, but not the eyes. Unlike albinism, it is caused by a reduction in multiple types of pigment, not just melanin.

This is an autosomal dominant hereditary condition, which tends to produce high rates of inheritance and long chains of generational transmission. All who inherit the gene have at some time in life evidence of piebald hypopigmentation of the hair or skin, most likely both. Historically, persons with extensive piebaldism have experienced abuse of the sort still suffered in the present by albinos, especially in Africa. This has ranged from display of unclothed African piebalds in "freak" shows and post cards of the early twentieth century to the forcing of piebalds (as in the case of albinos) to work long hours exposed to the sun (producing high rates of lethal skin cancers), to the use of piebald humans, including children, in risky medical experiments. The National Organization of Albinism and Hypopigmentation, as well as organizations such as Under the Same Sun, work to promote awareness of all forms of cutaneous variation and their medical implications, and to highlight human rights issues, especially the plight of albinos subject to extreme persecution in parts of Africa.

Piebaldism may be associated with the genes "KIT" or "SNAI2".

Melanism is a development of the dark-colored pigment melanin in the skin or its appendages and is the opposite of albinism. The word "melanism" is derived from the ("black pigment").

Pseudo-melanism, also called abundism, is another variant of pigmentation, characterized by dark spots or enlarged stripes, which cover a large part of the body of the animal, making it appear melanistic.

A deficiency in or total absence of melanin pigments is called amelanism.

The morbid deposition of black matter, often of a malignant character causing pigmented tumors, is called melanosis. For a description of melanin-related disorders, see melanin and ocular melanosis.

Oculocutaneous albinism (OCA) is a form of albinism involving the eyes (""), the skin ("-"), and according to some definitions, the hair.

Overall, an estimated 1 in 20,000 people worldwide are born with oculocutaneous albinism. OCA is caused by mutations in several genes that control the synthesis of melanin within the melanocytes.

Four types of oculocutaneous albinism have been described, all caused by a disruption of melanin synthesis and all autosomal recessive disorders.

OA1 is recognized by many different symptoms. Reduced visual acuity is accompanied by involuntary movements of the eye termed as nystagmus. Astigmatism is a condition wherein there occurs significant refractive error. Moreover, ocular albino eyes become crossed, a condition called as ‘lazy eyes’ or strabismus. Since very little pigment is present the iris becomes translucent and reflects light back. It appears green to blueish red. However, the most important part of the eye, the fovea which is responsible for acute vision, does not develop properly, probably indicating the role of melanin in the development stages of the eye. Some affected individuals may also develop photophobia/photodysphoria. All these symptoms are due to lack of pigmentation of the retina. Moreover, in an ocular albino eye, nerves from back of the eye to the brain may not follow the usual pattern of routing. In an ocular albino eye, more nerves cross from back of the eye to the opposite side of the brain instead of going to the both sides of the brain as in a normal eye. An ocular albino eye appears blueish pink in color with no pigmentation at all unlike a normal eye. Carrier women have regions of hypo- and hyper-pigmentation due to X-inactivation and partial iris transillumination and do not show any other symptoms exhibited by those affected by OA1.

In the beginning, medical officials defined ABCD syndrome by the four key characteristics of the syndrome. In the first case study of the Kurdish girl, researches described her as having "albinism and a black lock at the right temporo-occipital region along Blaschko lines, her eyelashes and brows were white, the irises in her eyes appeared to be blue, she had spots of retinal depigmentation, and she did not react to noise." The albinism is interesting in this diagnosis because the skin of an affected individual is albino pale besides the brown patches of mispigmented skin. The "black locks" described and seen in clinical pictures of the infants are thick patches of black hair above the ears that form a half circle reaching to the other ear to make a crest shape.

As identified in this first case study and stated in a dictionary of dermatologic syndromes, ABCD syndrome has many notable features, including "snow white hair in patches, distinct black locks of hair, skin white except brown macules, deafness, irises gray to blue, nystagmus, photophobia, poor visual activity, normal melanocytes in pigmented hair and skin, and absent melanocytes in areas of leukoderma." Individuals have the blue/gray irises typical of people affected by blindness. The C of ABCD syndrome is what distinguishes this genetic disorder from BADS and it involves cell migration disorder of the neurocytes of the gut. This characteristic occurs when nerve cells do not function correctly in the gut, which results in aganglionosis: The intestines’ failure to move food along the digestive tract. Deafness or being unresponsive to noise due to very low quality of hearing was reported in every case of ABCD syndrome. The characteristics of ABCD syndrome are clearly evident in an inflicted individual.

No longer considered a separate syndrome, ABCD syndrome is today considered to be a variation of Shah-Waardenburg type IV. Waardenburg syndrome (WS) is described as "the combination of sensorineural hearing loss, hypopigmentation of skin and hair, and pigmentary disturbances of the irides." Hearing loss and deafness, skin mispigmentation and albinism, and pigmentary changes in irises are the similarities between WS and ABCD. According to a dictionary of dermatologic syndromes, Waardenburg syndrome has many notable features, including "depigmentation of hair and skin – white forelock and premature graying of hair, confluent thick eyebrows, heterochromic irides or hypopigmentation of iris, laterally displaced inner canthi, congenital sensorineural deafness, broad nasal root, autosomal dominant disorder, and other associated findings, including black forelocks."

Ocular albinism type 1 (OA1), also called Nettleship–Falls syndrome, is the most common type of ocular albinism, with a prevalence rate of 1:50,000. It is an inheritable classical Mendelian type X-linked recessive disorder wherein the retinal pigment epithelium lacks pigment while hair and skin appear normal. Since it is usually an X-linked disorder, it occurs mostly in males, while females are carriers unless they are homozygous. About 60 missense and nonsense mutations, insertions, and deletions have been identified in "Oa1". Mutations in OA1 have been linked to defective glycosylation and thus improper intracellular transportation.

The eponyms of the name "Nettleship–Falls syndrome" are the ophthalmologists Edward Nettleship and Harold Francis Falls.

Leucism (occasionally spelled "leukism") is a general term for the phenotype resulting from defects in pigment cell differentiation and/or migration from the neural crest to skin, hair, or feathers during development. This results in either the entire surface (if all pigment cells fail to develop) or patches of body surface (if only a subset are defective) having a lack of cells capable of making pigment.

Since all pigment cell-types differentiate from the same multipotent precursor cell-type, leucism can cause the reduction in all types of pigment. This is in contrast to albinism, for which leucism is often mistaken. Albinism results in the reduction of melanin production only, though the melanocyte (or melanophore) is still present. Thus in species that have other pigment cell-types, for example xanthophores, albinos are not entirely white, but instead display a pale yellow colour.

More common than a complete absence of pigment cells is localized or incomplete hypopigmentation, resulting in irregular patches of white on an animal that otherwise has normal colouring and patterning. This partial leucism is known as a "pied" or "piebald" effect; and the ratio of white to normal-coloured skin can vary considerably not only between generations, but between different offspring from the same parents, and even between members of the same litter. This is notable in horses, cows, cats, dogs, the urban crow and the ball python but is also found in many other species.

A further difference between albinism and leucism is in eye colour. Due to the lack of melanin production in both the retinal pigmented epithelium (RPE) and iris, those affected by albinism typically have red eyes due to the underlying blood vessels showing through. In contrast, most leucistic animals have normally coloured eyes. This is because the melanocytes of the RPE are not derived from the neural crest, instead an outpouching of the neural tube generates the optic cup which, in turn, forms the retina. As these cells are from an independent developmental origin, they are typically unaffected by the genetic cause of leucism.

Genes that, when mutated, can cause leucism include, "c-kit", "mitf" and "EDNRB.

Tietz syndrome is characterized by profound hearing loss from birth, white hair and pale skin (hair color may darken over time to blond or red).

The hearing loss is caused by abnormalities of the inner ear (sensorineural hearing loss) and is present from birth. Individuals with Tietz syndrome often have skin and hair color that is lighter than those of other family members.

Tietz syndrome also affects the eyes. The iris in affected individuals is blue, and specialized cells in the eye called retinal pigment epithelial cells lack their normal pigment. The changes to these cells are generally detectable only by an eye examination; it is unclear whether the changes affect vision.

Tietz syndrome, also called Tietz albinism-deafness syndrome or albinism and deafness of Tietz, is an autosomal dominant congenital disorder characterized by deafness and leucism. It is caused by a mutation in the microphthalmia-associated transcription factor (MITF) gene. Tietz syndrome was first described in 1963 by Walter Tietz (1927–2003) a German Physician working in California.

ABCD syndrome is defined as albinism, black lock, cell migration disorder of the neurocytes of the gut, and deafness. It was initially misdiagnosed and later discovered that a homozygous mutation in the EDNRB gene causes ABCD syndrome. This helped scientists discover that it is the same as type IV Waardenburg syndrome, also known as Shah-Waardenburg syndrome.

Amelanism (also known as amelanosis) is a pigmentation abnormality characterized by the lack of pigments called melanins, commonly associated with a genetic loss of tyrosinase function. Amelanism can affect fish, amphibians, reptiles, birds, and mammals including humans. The appearance of an amelanistic animal depends on the remaining non-melanin pigments. The opposite of amelanism is melanism, a higher percentage of melanin.

A similar condition, albinism, is a hereditary condition characterised in animals by the absence of pigment in the eyes, skin, hair, scales, feathers or cuticle. This results in an all white animal, usually with pink or red eyes.

Ocular albinism is a form of albinism which, in contrast to oculocutaneous albinism, presents primarily in the eyes. There are multiple forms of ocular albinism, which are clinically similar.

Both known genes are on the X chromosome. When the term ""autosomal recessive ocular albinism"" ("AROA") is used, it usually refers to mild variants of oculocutaneous albinism rather than ocular albinism, which is "X-linked".

Theoretically, a mutation in any of the may cause disease, but below are some notable ones, with short description of symptoms:

- Adrenoleukodystrophy; leads to progressive brain damage, failure of the adrenal glands and eventually death.

- Alport syndrome; glomerulonephritis, endstage kidney disease, and hearing loss.

- Androgen insensitivity syndrome; variable degrees of undervirilization and/or infertility in XY persons of either gender

- Barth syndrome; metabolism distortion, delayed motor skills, stamina deficiency, hypotonia, chronic fatigue, delayed growth, cardiomyopathy, and compromised immune system.

- Blue cone monochromacy; low vision acuity, color blindness, photophobia, infantile nystagmus.

- Centronuclear myopathy; where cell nuclei are abnormally located in skeletal muscle cells. In CNM the nuclei are located at a position in the center of the cell, instead of their normal location at the periphery.

- Charcot–Marie–Tooth disease (CMTX2-3); disorder of nerves (neuropathy) that is characterized by loss of muscle tissue and touch sensation, predominantly in the feet and legs but also in the hands and arms in the advanced stages of disease.

- Coffin–Lowry syndrome; severe mental retardation sometimes associated with abnormalities of growth, cardiac abnormalities, kyphoscoliosis as well as auditory and visual abnormalities.

- Fabry disease; A lysosomal storage disease causing anhidrosis, fatigue, angiokeratomas, burning extremity pain and ocular involvement.

- Hunter's Syndrome; potentially causing hearing loss, thickening of the heart valves leading to a decline in cardiac function, obstructive airway disease, sleep apnea, and enlargement of the liver and spleen.

- Hypohidrotic ectodermal dysplasia, presenting with hypohidrosis, hypotrichosis, hypodontia

- Kabuki syndrome; multiple congenital anomalies and mental retardation.

- Spinal and bulbar muscular atrophy; muscle cramps and progressive weakness

- Lesch-Nyhan syndrome; neurologic dysfunction, cognitive and behavioral disturbances including self-mutilation, and uric acid overproduction (hyperuricemia)

- Lowe Syndrome; hydrophthalmia, cataracts, intellectual disabilities, aminoaciduria, reduced renal ammonia production and vitamin D-resistant rickets

- Menkes disease; sparse and coarse hair, growth failure, and deterioration of the nervous system

- Nasodigitoacoustic syndrome; mishaped nose, brachydactyly of the distal phalanges, sensorineural deafness

- Nonsyndromic deafness; hearing loss

- Norrie disease; cataracts, leukocoria along with other developmental issues in the eye

- Occipital horn syndrome; deformations in the skeleton

- Ocular albinism; lack of pigmentation in the eye

- Ornithine transcarbamylase deficiency; developmental delay and mental retardation. Progressive liver damage, skin lesions, and brittle hair may also be seen

- Siderius X-linked mental retardation syndrome; cleft lip and palate with mental retardation and facial dysmorphism, caused by mutations in the histone demethylase PHF8

- Simpson-Golabi-Behmel syndrome; coarse faces with protruding jaw and tongue, widened nasal bridge, and upturned nasal tip

- Spinal muscular atrophy caused by UBE1 gene mutation; weakness due to loss of the motor neurons of the spinal cord and brainstem

- Wiskott-Aldrich syndrome; eczema, thrombocytopenia, immune deficiency, and bloody diarrhea

- X-linked Severe Combined Immunodeficiency (SCID); infections, usually causing death in the first years of life

- X-linked sideroblastic anemia; skin paleness, fatigue, dizziness and enlarged spleen and liver.

All types of Griscelli syndrome have distinctive skin and hair coloring.

Type 1 is associated with eurological abnormalities. These include delayed development, intellectual disability, seizures, hypotonia and eye abnormalities.

Type 2 - unlike type 1 - is not associated primary neurological disease but is associated with an uncontrolled T lymphocyte expansion and macrophage activation syndrome. It is often associated with the hemophagocytic syndrome. This latter condition may be fatal in the absence of bone marrow transplantation.

Persons with type 3 have the typical light skin and hair coloring but are otherwise normal.

Griscelli syndrome is a rare autosomal recessive disorder characterized by albinism (hypopigmentation) with immunodeficiency, that usually causes death by early childhood.

Keloid, also known as keloid disorder and keloidal scar,

is the formation of a type of scar which, depending on its maturity, is composed mainly of either type III (early) or type I (late) collagen. It is a result of an overgrowth of granulation tissue (collagen type 3) at the site of a healed skin injury which is then slowly replaced by collagen type 1. Keloids are firm, rubbery lesions or shiny, fibrous nodules, and can vary from pink to the color of the person's skin or red to dark brown in color. A keloid scar is benign and not contagious, but sometimes accompanied by severe itchiness, pain, and changes in texture. In severe cases, it can affect movement of skin. Keloid scars are seen 15 times more frequently in people of African descent than in people of European descent.

Keloids should not be confused with hypertrophic scars, which are raised scars that do not grow beyond the boundaries of the original wound.

This syndrome consists a number of typical features. These include

- Agenesis of the corpus callosum (80-99% patients)

- Hypopigmentation of the eyes and hair (80-99% patients)

- Cardiomyopathy (80-99% patients)

- Combined immunodeficiency (80-99% patients)

- Muscular hypotonia (80-99% patients)

- Abnormality of retinal pigmentation (80-99% patients)

- Recurrent chest infections (80-99% patients)

- Abnormal EEG (80-99% patients)

- Intellectual disability (80-99% patients)

- Cataracts (75%)

- Seizures (65%)

- Renal abnormalities (15%)

Infections of the gastrointestinal and urinary tracts are common. Swallowing and feeding difficulties early on may result in a failure to thrive. Optic nerve hypoplasia, nystagmus and photophobia may occur. Facial dysmorphism (cleft lip/palate and micrognathia) and syndactyly may be present. Sensorineural hearing loss may also be present.

Death in infancy is not uncommon and is usually due to cardiac complications or severe infections.

Oculocutaneous Albinism Type I or –Type 1A (OCA1A) is an autosomal recessive skin disease associated with albinism. This type of albinism is caused when the gene OCA1 does not function properly.

The location of OCA1 may be written as "11q1.4-q2.1", meaning it is on chromosome 11, long arm, somewhere in the range of band 1, sub-band 4, and band 2, sub-band 1.

Griscelli syndrome is defined by the characteristic hypopigmentation, with frequent pyogenic infection, enlargement of the liver and spleen, a low blood neutrophil level, low blood platelet level, and immunodeficiency. Very often there is also impaired natural killer cell activity, absent delayed-type hypersensitivity and a poor cell proliferation response to antigenic challenge. This may be caused by the loss of three different genes, each of which has different additional effects, resulting in three types of syndrome. Its inheritance is autosomal recessive.

Examination of the hair in this syndrome may be useful. Under light microscopy, these hairs exhibit bigger and irregular melanin granules, distributed mainly near the medulla. Under polarized light microscopy, the hairs appear monotonously white.

In medicine, heterotopia is the presence of a particular tissue type at a non-physiological site, but usually co-existing with original tissue in its correct anatomical location. In other words, it implies ectopic tissue, in addition to retention of the original tissue type. In neuropathology, for example, gray matter heterotopia is the presence of gray matter within the cerebral white matter or ventricles. Heterotopia within the brain is often divided into three groups: subependymal heterotopia, focal cortical heterotopia and band heterotopia. Another example is a Meckel's diverticulum, which may contain heterotopic gastric or pancreatic tissue.

In biology specifically, "heterotopy" refers to an altered location of trait expression. In her book "Developmental Plasticity and Evolution", Mary-Jane West Eberhard has a cover art of the sulphur crested cockatoo and comments on the back cover "Did long crest[head] feathers evolve by gradual modification of ancestral head feathers? Or are they descendants of wing feathers, developmentally transplanted onto the head". This idea sets the tone for the rest of her book which goes into depth about developmental novelties and their relation to evolution. Heterotopy is a somewhat obscure but well demonstrated example of how developmental change can lead to novel forms. The central concept is that a feature seen in one area of an organism has had its location changed in evolutionary lineages.

Keloids expand in claw-like growths over normal skin. They have the capability to hurt with a needle-like pain or to itch, although the degree of sensation varies from person to person.

If the keloid becomes infected, it may ulcerate. Removing the scar is one treatment option; however, it may result in more severe consequences: the probability that the resulting surgery scar will also become a keloid is high, usually greater than 50%. Laser treatment has also been used with varying degrees of success.

Keloids form within scar tissue. Collagen, used in wound repair, tends to overgrow in this area, sometimes producing a lump many times larger than that of the original scar. They can also range in color from pink to red. Although they usually occur at the site of an injury, keloids can also arise spontaneously. They can occur at the site of a piercing and even from something as simple as a pimple or scratch. They can occur as a result of severe acne or chickenpox scarring, infection at a wound site, repeated trauma to an area, excessive skin tension during wound closure or a foreign body in a wound. Keloids can sometimes be sensitive to chlorine. Keloid scars can grow, if they appear at a younger age, because the body is still growing.