With 73 cat breeds recognized by the International Cat Association, it can be difficult to discern a Ragdoll from a Ragamuffin.

Most of us, though, can pick out a Siamese cat. Known for their dark eye masks, socks, and tail—called “points”—that stand out against their cream-colored bodies and sparkling blue eyes, the Siamese is one of the world’s easily recognized breeds.

Those trademark points stem from a genetic mutation known as the Himalayan gene, which was discovered in the breed in 2005. This recessive gene, passed down from both parents, also gives the felines temperature-sensitive fur that can change color.

In the womb, Siamese kittens develop at temperatures of about 101 Fahrenheit, a cat’s normal temperature. Once born, all-white kittens eventually begin to cool at their extremities, such as their tail, legs, ears ,and face. These lower temperatures cause the Himalayan gene to activate the body’s melanin, a pigment also found in people. That’s why a Siamese cat’s warmer bodies stay light, but their cooler parts become darker as they mature. (Read how tabbies get their stripes.)

“You can see them change,” says Betsy Arnold, a veterinarian who runs a cats-only practice in Rochester, New York, and started breeding Siamese when she was in her teens.

At about two weeks old, Arnold says, dark hues begin to spread to their limbs. By about a month old, their final color emerges, which may be one of several varieties, among them blue point, lilac point, chocolate point, and seal point, which has a light, cream-colored coat with dark brown hues on its paws, tail, nose, and ears.

A lifelong influence

The Himalayan mutation naturally occurs in South Asian domestic cats, says Leslie Lyons, a feline geneticist at the University of Missouri who first identified the mutation in Siamese cats. 

Over time, as people selectively bred cats with the striking pale color and dark points, they passed the gene to different breeds, such as Siamese, Birmans, Ragdolls, and Burmese. Mixed breeds can also carry the genetic mutation.

These cats’ vibrant blue eyes are also due to the Himalayan gene, which influences their eye pigment. (See vintage pictures of pampered pets.)

The Himalayan mutation causes fur to darken as the cat ages, though any sort of trauma or change to the cat’s fur can alter its hues.

If a Siamese cat has surgery, for example, an area of fur that was shaved may grow back darker because the impacted area is cooler while the hair grows back. Eventually, the fur may become lighter again, Arnold says.

In the 1920s, a Siamese cat living in Moscow that wore a jacket over a shaved shoulder had its fur grow back all white, since that area was kept warmer. The fur later turned darker again, according to the University of Alaska.

Health concerns

Many other species have the Himalayan gene, including Himalayan rabbits, says Lyons.

Domestic rats, color-pointed gerbils, and American minks can also carry the mutation. In 2021 the journal Gene reported a dachshund with a different mutation on the same Himalayan gene that produced Siamese-type coloration, a rare occurrence in dogs, Lyons says.

“Each species has its own mutation in the same gene, but then have been bred to have the specific coloration,” she says. (Read surprising things you never knew about your cat.)

While there’s no overarching advantage or disadvantage to the mutation in these domestic animals, Lyons says, it “does come with some health concerns, too,” including eye issues.

Siamese often have crossed or misaligned eyes, also called strabismus, which can compromise vision as well as depth perception.

Even if the cat’s eyes are aligned, the animal may still suffer from nystagmus, or shaking eyes, a condition in which the eye sometimes dart slightly from side to side in repetitive, uncontrolled movements that can cause vision or even balance problems, says Arnold. She adds she hasn’t seen the condition in her practice.

Both Lyons and Arnold recommend pet owners get their Siamese pets from reputable breeders, or adopt them from a rescue. Wherever they’re from, though, both experts agree these masked felines will steal anyone’s heart.