Keratin and Keratosis

Keratin is a fibrous structural protein of hair, nails, horn, hoofs, wool, feathers, and of the epithelial cells in the outermost layers of the skin. The polypeptide chains of keratin are arranged in parallel sheets held together by hydrogen bonding.

Keratosis is a growth of keratin on the skin. More specifically, it can refer to:

* actinic keratosis (also known as solar keratosis)
* seborrheic keratosis
* keratosis pilaris (KP), also known as (follicular keratosis)

Actinic keratosis (also called solar keratosis, or AK) is a premalignant condition of thick, scaly, or crusty patches of skin. It is more common in fair-skinned people. It is associated with those who are frequently exposed to the sun, as it is usually accompanied by solar damage. Since some of these pre-cancers progress to squamous cell carcinoma, they should be treated.

When skin is exposed to the sun constantly, thick, scaly, or crusty bumps appear. The scaly or crusty part of the bump is dry and rough. The growths start out as flat scaly areas, and later grow into a tough, wart-like area.

An actinic keratosis site commonly ranges between 2 and 6 millimeters in size, and can be dark or light, tan, pink, red, a combination of all these, or have the same pigment as the surrounding skin. It may appear on any sun-exposed area, such as the face, ears, neck, scalp, chest, backs of hands, forearms, or lips.

A seborrheic keratosis (also known as "Seborrheic verruca," "Senile keratosis," and "Senile wart") is a noncancerous benign skin growth that originates in keratinocytes. Like liver spots, seborrheic keratoses are seen more often as people age. In fact they are sometimes humorously referred to as the "barnacles of old age".

They appear in various colors, from light tan to black. They are round or oval, feel flat or slightly elevated (like the scab from a healing wound), and range in size from very small to more than 2.5 centimetres (1.0 in) across. They can resemble warts, though they have no viral origins. They can also resemble melanoma skin cancer, though they are unrelated to melanoma as well. Because only the top layers of the epidermis are involved, seborrheic keratoses are often described as having a "pasted on" appearance.

Keratosis pilaris (KP, also follicular keratosis) is a very common genetic follicular condition that is manifested by the appearance of rough bumps on the skin, hence referred to as chicken skin. It most often appears on the back and outer sides of the upper arms (though the lower arms can also be affected), and can also occur on the thighs and tops of legs, flanks, buttocks, or any body part except glabrous skin (like the palms or soles of feet). Less commonly, lesions appear on the face, which may be mistaken for acne.

Keratins are tough and insoluble, they form the hard but mineralized structures found in reptiles, birds, amphibians, and mammals. They are rivaled as biological materials in toughness only by chitin.

Keratins are the main constituent of structures that grow from the skin:

* the α-keratins in the hair (including wool), horns, nails, claws and hooves of mammals
* the harder β-keratins found in nails and in the scales and claws of reptiles, their shells (chelonians, such as tortoise, turtle, terrapin), and in the feathers, beaks, claws of birds and quills of porcupines. (These keratins are formed primarily in beta sheets. However, beta sheets are also found in α-keratins.)

* Arthropods such as crustaceans often have parts of their armor or exoskeleton made of keratin, sometimes in combination with chitin.

* The baleen plates of filter-feeding whales are made of keratin.

* They can be integrated in the chitinophosphatic material that makes up the shell and setae in many brachiopods.

* Keratins are also found in the gastrointestinal tracts of many animals, including roundworms (which also have an outer layer made of keratin).

* Although it is now difficult to be certain, the scales, claws, some protective armour and the beaks of dinosaurs would, almost certainly, have been composed of a type of keratin.

* In Crossopterygian fish, the outer layer of cosmoid scales was keratin.

The amino acids which combine to form keratin have several unique properties.

Of the amino acids in keratin, cystine may account for as much as 24 percent. The numerous disulfide bonds formed by cystine are responsible for the great stability of keratin: it is completely insoluble in hot or cold water and is not attacked by proteolytic enzymes (the enzymes that cleave protein molecules).

The length of keratin fibres depends on their water content: complete hydration (approximately 16 percent water) increases their length by 10 to 12 percent.

Depending on the levels of the various amino acids, keratin can be inflexible and hard, like hooves, or soft, as is the case with skin. Most of the keratin that people interact with is actually dead; hair, skin, and nails are all formed from dead cells which the body sheds as new cells push up from underneath. If the dead cells are kept in good condition, they will serve as an insulating layer to protect the delicate new keratin below them.

Keratin is difficult to dissolve, because it contains cysteine disulfide, which means that it is able to form disulfide bridges. These disulfide bridges create a helix shape that is extremely strong, as sulfur atoms bond to each other from across the helix, creating a fibrous matrix which is not readily soluble. Depending on how much cysteine disulfide keratin contains, the bond can be very very strong to make hard cells like those found in hooves, or it can be softer to make flexible keratin like hair and skin.

Because of the high levels of sulfur in keratin, when it is burned it emits a distinct sulfurous odor which some people find distasteful.

Keratin is formed by keratinocytes, living cells which make up a large part of skin, hair, nails, and other keratin containing parts of the body. The cells slowly push their way upwards, eventually dying and forming a protective layer of cells. Thousands of these cells are shed every day, and the process can be accelerated by various medical conditions, such as psoriasis. Damage to the external layer of keratin can cause skin, hair, and nails to look unhealthy or flaky.

Hair and nails on humans especially tend to become dry and brittle, because the dead keratin is being pushed to great lengths. By eating foods like gelatin and keeping hair and nails moist, they can be grown out while still remaining healthy.

In general, the thicker the layer of keratin, the healthier the hair or nail is, because the dead cells outside protect the living cells at the core. Keeping the external layer of keratin moisturized will also keep it healthy and prevent cracking and splitting, whether the keratin is forming the hooves of a horse or the skin of a human.

Keratosis pilaris is a skin condition usually seen on the buttocks, thighs and buttocks, though not limited to these areas alone.

Keratosis pilaris is caused by the build-up of keratin in the openings of the skin’s hair follicles, which causing hyperkeratization, and forming plugs out of the follicles. Keratin is a protein that protects skin from infection and harmful substances. Keratin build-up is still currently unknown although too much production of keratin may be related to a person’s genetic make-up or other skin conditions such as atopic dermatitis or ichthyosis vulgaris. It is a harmless condition, hereditary in nature, and can’t be transmitted from person to person. It is also most prevalent during the winter months compared to the summer.

Keratosis pilaris usually appear as small, red or white zits or rough patches that feel rough and dry. In common cases, they are neither painful nor itchy. It is commonly confused with acne because of the rough bumps on the skin, not unlike what goose bumps look like.

Keratosis pilaris is usually common in babies and teenagers. For teenagers, this pimple-like growths are commonly seen on the upper arms and thighs; for babies, it usually grows on their cheeks. If left untreated, keratosis pilaris may linger for years; it would only start to gradually disappear before the age of 30.