Dysmelia can be caused by

- inheritance of abnormal genes, e.g. polydactyly, ectrodactyly or brachydactyly, symptoms of deformed limbs then often occur in combination with other symptoms (syndromes)

- external causes during pregnancy (thus not inherited), e.g. via amniotic band syndrome

- teratogenic drugs (e.g. thalidomide, which causes phocomelia) or environmental chemicals

- ionizing radiation (nuclear weapons, radioiodine, radiation therapy)

- infections

- metabolic imbalance

A low socioeconomic status in a deprived neighborhood may include exposure to “environmental stressors and risk factors.” Socioeconomic inequalities are commonly measured by the Cartairs-Morris score, Index of Multiple Deprivation, Townsend deprivation index, and the Jarman score. The Jarman score, for example, considers “unemployment, overcrowding, single parents, under-fives, elderly living alone, ethnicity, low social class and residential mobility.” In Vos’ meta-analysis these indices are used to view the effect of low SES neighborhoods on maternal health. In the meta-analysis, data from individual studies were collected from 1985 up until 2008. Vos concludes that a correlation exists between prenatal adversities and deprived neighborhoods. Other studies have shown that low SES is closely associated with the development of the fetus in utero and growth retardation. Studies also suggest that children born in low SES families are “likely to be born prematurely, at low birth weight, or with asphyxia, a birth defect, a disability, fetal alcohol syndrome, or AIDS.” Bradley and Corwyn also suggest that congenital disorders arise from the mother’s lack of nutrition, a poor lifestyle, maternal substance abuse and “living in a neighborhood that contains hazards affecting fetal development (toxic waste dumps).” In a meta-analysis that viewed how inequalities influenced maternal health, it was suggested that deprived neighborhoods often promoted behaviors such as smoking, drug and alcohol use. After controlling for socioeconomic factors and ethnicity, several individual studies demonstrated an association with outcomes such as perinatal mortality and preterm birth.

Substances whose toxicity can cause congenital disorders are called "teratogens", and include certain pharmaceutical and recreational drugs in pregnancy as well as many environmental toxins in pregnancy.

A review published in 2010 identified 6 main teratogenic mechanisms associated with medication use: folate antagonism, neural crest cell disruption, endocrine disruption, oxidative stress, vascular disruption and specific receptor- or enzyme-mediated teratogenesis.

It is estimated that 10% of all birth defects are caused by prenatal exposure to a teratogenic agent. These exposures include, but are not limited to, medication or drug exposures, maternal infections and diseases, and environmental and occupational exposures. Paternal smoking use has also been linked to an increased risk of birth defects and childhood cancer for the offspring, where the paternal germline undergoes oxidative damage due to cigarette use. Teratogen-caused birth defects are potentially preventable. Studies have shown that nearly 50% of pregnant women have been exposed to at least one medication during gestation. During pregnancy, a female can also be exposed to teratogens from the contaminated clothing or toxins within the seminal fluid of a partner. An additional study found that of 200 individuals referred for genetic counseling for a teratogenic exposure, 52% were exposed to more than one potential teratogen.

When an individual is born with phocomelia due to drugs or pharmaceuticals, it is known as thalidomide syndrome. The symptoms of thalidomide syndrome are defined by absent or shortened limbs; causing flipper hands and feet. According to Anthony J Perri III, and Sylvia Hsu they can additionally receive:

- Palsy disorder of the face

- Ear and eye abnormalities; resulting in limited/complete loss of hearing or sight

- Gastrointestinal and genitourinary tract disorders

- Ingrown genitalia

- Undeveloped/missing lungs

- Distorted digestive tract, heart, kidney

- disorders to the limbs

The infants that were exposed to thalidomide during development phases had a 40% chance of survival. The McMredie-McBride hypothesis explains that the limbs of the infants become malformed as a result of the thalidomide harming the neural tissue—simply because the neural tissue has such a large impact on formation and development of the limbs.

According to National Organization for Rare Disorders (NORD): when phocomelia is transmitted [in its familial genetic form] it is seen as an autosomal recessive trait and the mutation is linked to chromosome 8.

A study of Roberts Syndrome, a genetic disorder showing similar symptoms to phocomelia, has shed light on the possible causes. An individual afflicted with Roberts Syndrome will have chromosome copies that do not connect at the centromeres, making them unable to line up accordingly. As a result, the newly made cells contain an excess or reduced number of chromosomes. In both Roberts Syndrome and phocomelia the cells cease to develop, or die, preventing proper development of the limbs, eyes, brain, palate, or other structures.

Dysmelia can refer to

- missing (aplasia) limbs: amelia, oligodactyly, congenital amputation e.g. Tibial or Radial aplasia

- malformation of limbs: shortening (micromelia, rhizomelia or mesomelia), ectrodactyly, phocomelia, meromelia, syndactyly, brachydactyly, club foot

- too many limbs: polymelia, polydactyly, polysyndactyly

- others: Tetraamelia, hemimelia, Symbrachydactyly

Oligodactyly (from the Ancient Greek "oligos" meaning "few" and δάκτυλος "daktylos" meaning "finger") is the presence of fewer than five fingers or toes on a hand or foot.

It is quite often incorrectly called "hypodactyly", but the Greek prefixes and are used for scales (e.g. in hypoglycaemia and hypercholesterolemia). This as opposed to or scales, where and should be used (e.g. in oligarchy and polygamy). Oligodactyly is therefore the opposite of polydactyly. Very rare, this medical condition usually has a genetic or familial cause.

Oligodactyly is sometimes a sign or symptom of several syndromes including Poland syndrome and Weyer Ulnar Ray Syndrome. It is a type of Dysmelia.

Ectrodactyly is an extreme instance of oligodactyly, involving the absence of one or more central digits of the hand or foot and is also known as split hand/split foot malformation (SHFM). The hands and feet of people with ectrodactyly are often described as "claw-like" and may include only the thumb and one finger (usually either the little finger, ring finger, or a syndactyly of the two) with similar abnormalities of the feet.

People with oligodactyly often have full use of the remaining digits and adapt well to their condition. They are not greatly hindered in their daily activities, if at all. Even those with the most extreme forms are known to engage in tasks that require fine control, such as writing and bootmaking as well as working as a cab driver.

Vadoma people of Zimbabwe have a high frequency of oligodactyly.

In the above brachydactyly syndromes, short digits are the most prominent of the anomalies, but in many other syndromes (Down syndrome, Rubinstein-Taybi syndrome, etc.), brachydactyly is a minor feature compared to the other anomalies or problems comprising the syndrome.

Brachydactyly (Greek βραχύς = "short" plus δάκτυλος = "finger"), is a medical term which literally means "shortness of the fingers and toes" (digits). The shortness is relative to the length of other long bones and other parts of the body. Brachydactyly is an inherited, usually dominant trait. It most often occurs as an isolated dysmelia, but can also occur with other anomalies as part of many congenital syndromes.

Nomograms for normal values of finger length as a ratio to other body measurements have been published. In clinical genetics the most commonly used index of digit length is the dimensionless ratio of the length of the 3rd (middle) finger to the hand length. Both are expressed in the same units (centimeters, for example) and are measured in an open hand from the fingertip to the principal creases where the finger joins the palm and where the palm joins the wrist.

Polymelia (from Greek πολυ- = "many" plus μέλος (plural μέλεα) = "limb") also known as "hydra syndrome" is a birth defect involving limbs (a type of dysmelia), in which the affected individual has more than the usual number of limbs. In humans and most land-dwelling animals, this means having five or more limbs. The extra limb is most commonly shrunken and/or deformed.

Sometimes an embryo started as conjoined twins, but one twin degenerated completely except for one or more limbs, which end up attached to the other twin.

Sometimes small extra legs between the normal legs are caused by the body axis forking in the dipygus condition.

Many mythological creatures like dragons, winged horses, and griffins have six limbs: four legs and two wings. The dragon's science is discussed in "Dragons: A Fantasy Made Real".

In Greek Mythology, the Hekatonkheires were said to each have one hundred hands. The Gegenees were a race of giants with six arms.

Sleipnir, Odin's horse in Norse mythology, has eight normal horse legs, and is usually depicted with limbs twinned at the shoulder or hip.

Several Hindu deities are depicted with multiple arms and sometimes also multiple legs.