Fur is a thick growth of hair that covers the skin of many animals. It is a defining characteristic of mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture and the underfur acts as an insulating blanket that keeps the animal warm.^[1]

The fur of mammals has many uses: protection, sensory purposes, waterproofing, and camouflage, with the primary usage being thermoregulation.^[2] The types of hair include definitive, which may be shed after reaching a certain length; vibrissae, which are sensory hairs and are most commonly whiskers; pelage, which consists of guard hairs, under-fur, and awn hair; spines, which are a type of stiff guard hair used for defense in, for example, porcupines; bristles, which are long hairs usually used in visual signals, such as the mane of a lion; velli, often called "down fur," which insulates newborn mammals; and wool, which is long, soft, and often curly.^{[3] []} Hair length is negligible in thermoregulation, as some tropical mammals, such as sloths, have the same fur length as some arctic mammals but with less insulation; and, conversely, other tropical mammals with short hair have the same insulating value as arctic mammals. The denseness of fur can increase an animal's insulation value, and arctic mammals especially have dense fur; for example, the musk ox has guard hairs measuring 30 cm (12 in) as well as a dense underfur, which forms an airtight coat, allowing them to survive in temperatures of −40 °C (−40 °F).^{[3] []} Some desert mammals, such as camels, use dense fur to prevent solar heat from reaching their skin, allowing the animal to stay cool; a camel's fur may reach 70 °C (158 °F) in the summer, but the skin stays at 40 °C (104 °F).^{[3] []} Aquatic mammals, conversely, trap air in their fur to conserve heat by keeping the skin dry.^{[3] []}

Mammalian coats are colored for a variety of reasons, the major selective pressures including camouflage, sexual selection, communication, and physiological processes such as temperature regulation. Camouflage is a powerful influence in many mammals, as it helps to conceal individuals from predators or prey.^[4] Aposematism, warning off possible predators, is the most likely explanation of the black-and-white pelage of many mammals which are able to defend themselves, such as in the foul-smelling skunk and the powerful and aggressive honey badger.^[5] In arctic and subarctic mammals such as the arctic fox (Alopex lagopus), collared lemming (Dicrostonyx groenlandicus), stoat (Mustela erminea), and snowshoe hare (Lepus americanus), seasonal color change between brown in summer and white in winter is driven largely by camouflage.^[6] Differences in female and male coat color may indicate nutrition and hormone levels, important in mate selection.^[7] Some arboreal mammals, notably primates and marsupials, have shades of violet, green, or blue skin on parts of their bodies, indicating some distinct advantage in their largely arboreal habitat due to convergent evolution.^[8] The green coloration of sloths, however, is the result of a symbiotic relationship with algae.^[9] Coat color is sometimes sexually dimorphic, as in many primate species.^[10] Coat color may influence the ability to retain heat, depending on how much light is reflected. Mammals with a darker colored coat can absorb more heat from solar radiation, and stay warmer, and some smaller mammals, such as voles, have darker fur in the winter. The white, pigmentless fur of arctic mammals, such as the polar bear, may reflect more solar radiation directly onto the skin.^{[3] [] [2]}

The term pelage – first known use in English c. 1828 (French, from Middle French, from poil for "hair", from Old French peilss, from Latin pilus^[11]) – is sometimes used to refer to an animal's complete coat. The term fur is also used to refer to animal pelts which have been processed into leather with their hair still attached. The words fur or furry are also used, more casually, to refer to hair-like growths or formations, particularly when the subject being referred to exhibits a dense coat of fine, soft "hairs". If layered, rather than grown as a single coat, it may consist of short down hairs, long guard hairs, and in some cases, medium awn hairs. Mammals with reduced amounts of fur are often called "naked", as with the naked mole-rat, or "hairless", as with hairless dogs.

An animal with commercially valuable fur is known within the fur industry as a furbearer.^[12] The use of fur as clothing or decoration is controversial; animal welfare advocates object to the trapping and killing of wildlife, and to the confinement and killing of animals on fur farms.

The modern mammalian fur arrangement is known to have occurred as far back as docodonts, haramiyidans and eutriconodonts, with specimens of Castorocauda, Megaconus and Spinolestes preserving compound follicles with both guard hair and underfur.

Fur may consist of three layers, each with a different type of hair.

Down hair (also known as underfur, undercoat or ground hair) is the bottom—or inner—layer, composed of wavy or curly hairs with no straight portions or sharp points. Down hairs, which are also flat, tend to be the shortest and most numerous in the coat. Thermoregulation is the principal function of the down hair, which insulates a layer of dry air next to the skin.

The awn hair can be thought of as a hybrid, bridging the gap between the distinctly different characteristics of down and guard hairs. Awn hairs begin their growth much like guard hairs, but less than half way to their full length, awn hairs start to grow thin and wavy like down hair. The proximal part of the awn hair assists in thermoregulation (like the down hair), whereas the distal part can shed water (like the guard hair). The awn hair's thin basal portion does not allow the amount of piloerection that the stiffer guard hairs are capable of. Mammals with well developed down and guard hairs also usually have large numbers of awn hairs, which may even sometimes be the bulk of the visible coat.

Guard hair is the top—or outer—layer of the coat. Guard hairs are longer, generally coarser, and have nearly straight shafts that protrude through the layer of softer down hair. The distal end of the guard hair is the visible layer of most mammal coats. This layer has the most marked pigmentation and gloss, manifesting as coat markings that are adapted for camouflage or display. Guard hair repels water and blocks sunlight, protecting the undercoat and skin in wet or aquatic habitats, and from the sun's ultraviolet radiation. Guard hairs can also reduce the severity of cuts or scratches to the skin. Many mammals, such as the domestic dog and cat, have a pilomotor reflex that raises their guard hairs as part of a threat display when agitated.

Hair is one of the defining characteristics of mammals; however, several species or breeds have considerably reduced amounts of fur. These are often called "naked" or "hairless".

Some mammals naturally have reduced amounts of fur. Some semiaquatic or aquatic mammals such as cetaceans, pinnipeds and hippopotamuses have evolved hairlessness, presumably to reduce resistance through water. The naked mole-rat has evolved hairlessness, perhaps as an adaptation to their subterranean life-style. Two of the largest extant mammals, the elephant and the rhinoceros, are largely hairless. The hairless bat is mostly hairless but does have short bristly hairs around its neck, on its front toes, and around the throat sac, along with fine hairs on the head and tail membrane. Most hairless animals cannot go in the sun for long periods of time, or stay in the cold for too long.^[13]

Humans are the only primate species that have undergone significant hair loss. The hairlessness of humans compared to related species may be due to loss of functionality in the pseudogene KRTHAP1 (which helps produce keratin)^[14] Although the researchers dated the mutation to 240 000 ya, both the Altai Neandertal and Denisovan have the loss-of-function mutation, indicating it is much older. Mutations in the gene HR can lead to complete hair loss, though this is not typical in humans.^[15]

Sheep have not become hairless; however, their pelage is usually referred to as "wool" rather than fur.

At times, when a hairless domesticated animal is discovered, usually owing to a naturally occurring genetic mutation, humans may intentionally inbreed those hairless individuals and, after multiple generations, artificially create breeds that are hairless. There are several breeds of hairless cats, perhaps the most commonly known being the Sphynx cat. Similarly, there are several breeds of hairless dogs. Other examples of artificially selected hairless animals include the hairless guinea-pig, nude mouse, and the hairless rat.

Fur has long served as a source of clothing for humans, including Neanderthals. Historically, it was worn for its insulating quality, with aesthetics becoming a factor over time. Pelts were worn in or out, depending on their characteristics and desired use. Today fur and trim used in garments may be dyed bright colors or to mimic exotic animal patterns, or shorn close like velvet. The term "a fur" may connote a coat, wrap, or shawl.

The manufacturing of fur clothing involves obtaining animal pelts where the hair is left on the animal's processed skin. In contrast, making leather involves removing the hair from the hide or pelt and using only the skin. The use of wool involves shearing the animal's fleece from the living animal, so that the wool can be regrown but sheepskin shearling is made by retaining the fleece to the leather and shearing it.^[16] Shearling is used for boots, jackets and coats and is probably the most common type of skin worn.

Fur is also used to make felt. A common felt is made from beaver fur and is used in high-end cowboy hats.^[17]

Common furbearers used include fox, rabbit, mink, beaver, ermine, otter, sable, seal, coyote, chinchilla, raccoon, and possum.

The import and sale of seal products was banned in the U.S. in 1972 over conservation concerns about Canadian seals. The import and sale is still banned even though the Marine Animal Response Society estimates the harp seal population is thriving at approximately 8 million.^[18] The import, export and sales of domesticated cat and dog fur were also banned in the U.S. under the Dog and Cat Protection Act of 2000.^[19]

Fur clothing predates written history and has been recovered from various archaeological sites worldwide. Crown proclamations known as “sumptuary legislation” were issued in England^[20] limiting the wearing of certain furs to the higher social statuses, thereby establishing a cachet based on exclusivity. Furs such as marten, grey squirrel and ermine were reserved for the aristocracy, while fox, hare and beaver clothed the middle, and goat, wolf and sheepskin the lower. Fur was primarily used for visible linings, with species varied by season within social classes. Furbearing animals decreased in West Europe and began to be imported from the Middle East and Russia.^[21]

As new kinds of fur entered Europe, other uses were made with fur other than clothing. Beaver was most desired but used to make hats which became a popular headpiece especially during the wartime. Swedish soldiers wore broad-brimmed hats made exclusively from beaver felt. Due to the limitations of beaver fur, hat-makers relied heavily on North America for imports as beaver was only available in the Scandinavian peninsula.^[21]

Other than the military, fur has been used for accessories such as hats, hoods, scarves, and muffs. Design elements including the visuals of the animal were considered acceptable with heads, tails and paws still being kept on the accessories. During the nineteenth century, seal and karakul were made into indoor jackets. The twentieth century was the beginning of the fur coats being fashionable in West Europe with full fur coats. With lifestyle changes as a result of developments like indoor heating, the international textile trade affected how fur was distributed around the world. Europeans focused on using local resources giving fur association with femininity with the increasing use of mink. In 1970, Germany was the world’s largest fur market. The International Fur Trade Federation banned endangering species furs like silk monkey, ocelot, leopard, tiger, and polar bear in 1975. The use of animal skins were brought to light during the 1980s by animal right organisations and the demand for fur decreased. Anti-fur organisations raised awareness of the controversy between animal welfare and fashion. Fur farming became banned in Britain in 1999. During the twenty-first century, fox and mink have been bred in captivity with Denmark, Holland and Finland being leaders of mink production.^[20]

Most of the fur sold by high fashion retailers globally is from farmed animals such as mink, foxes, and rabbits. Cruel methods of killing have made people more aware as the animal rights activists work harder to protect the animals. The recommendations (2001) of the European Commission’s Scientific Committee on Animal Health and Animal Welfare (SCAHAW) state correspondingly: ‘In comparison with other farm animals, species farmed for their fur have been subjected to relatively little active selection except with respect to fur characteristics. ^{[22] [23]}

Fur factories are extremely harmful to soil hence environmentally devastating. The process of fur manufacturing includes waterways-pumping waste and the toxic chemicals in to the surrounding environment. There are serious environmental issues on both sides whether the fur is fake or real. Faux fur uses harmful chemicals, cheaper labor hence able to sell at lower prices. Faux fur adds to the waste produced by fast fashion, including microfiber pollution in the ocean. As a petroleum product, fake fur fibers do not biodegrade easily and the dyeing process uses a lot chemicals that are seeped into the oceans and rivers causing water and ocean pollution. Real fur, on the other hand, is naturally biodegradable and can be passed down for generations although the cost is the inhumane treatment of animals. ^[24]

Intro of alternatives in the early 20th century brought tension to clothing industry as the faux fur manufacturers started producing faux fur and capitalising on profits. By 1950s synthetic fur garments had become extremely popular and affordable. Newspapers were writing articles on major chemical companies trying to out do each other in the quest to create the most realistic fake fur.^[25]

The popularity of natural fur has gone up and down in recent years. Vogue Paris published a homage to fur in August 2017 and later Gucci followed the idea of not using animal fur other high end brands to follow this lead are Stella McCartney, Givenchy, Calvin Klein, Ralph Lauren, Michael Kors, Philosophy di Lorenzo Serafini. Burberry announced to stop sending model with fur on runways however did not stop selling it in stores. There are many companies that are taking the imitative of coming up with more sustainable ways in producing leather and fur. Designer Ingar Helgason is developing Bio fur which would grows synthetic pelts the way that Modern Meadow has been able to produce grown leather and Diamond foundry created lab grown diamonds. BOF fur debate hosted by Zilberkweit director of the British Fur Association argued that natural fur was more sustainable, many forms of faux fur are not biodegradable “Our industry is about raising animals in a natural way, a kind way and it’s a renewable source. However not everyone agrees to this others said that chemical processes needed to treat animals’ fur in order to be worn are just as detrimental to the environment.^{[26] [27]}

PETA representative Johanna Fuoss credits social media and email marketing campaigns for helping to mobilize an unprecedented number of animal rights activists. “In the year before Michael Kors stopped using fur, he had received more than 150,000 emails,” Fuoss tells Highsnobiety. “This puts a certain pressure on designers who can see that the zeitgeist is moving away from fur. ”New technologies and platforms have made it easier than ever for those advocating change to get results. While in the past, activists had to invade runways with signs and paint, or physically mail privately viewed letters, today’s activist can raise a commotion without leaving the house.^[28][26][29]

In spite of organized backlash against it, the fur market in 2016 was $30 billion. Heritage fashion houses such as Hermès, Dior and Chanel still use natural fur. Alex Mcintosh, who leads the Fashion Futures post grad program at London College of Fashion, says “Change on this level would only be driven on a genuine lack of demand and not just social media outcry”. As McIntosh puts it, “The choice not to sell fur is not an environmental decision. “People conflating not selling fur with sustainability is quite dangerous, because they are not the same thing. It’s not a choice that is about sustainability, it’s a choice about ethics and what you think is acceptable in terms of animal welfare.”^[27]