A white cat with blue eyes is striking enough that people have built myths around it for centuries. The deafness that often comes with that combination is not a myth, it is one of the better-documented genetic links in feline biology, and understanding it changes how you read your cat's behaviour.
The gene that does two jobs at once
The white coat in cats is most commonly produced by a dominant gene called W, or White. This gene suppresses the expression of every other colour gene the cat carries, which is why a white cat can have kittens of almost any colour depending on what is hidden underneath. But the W gene does something else as well: it affects melanocytes, the pigment-producing cells that migrate through the body during foetal development.
Melanocytes do not only make colour. In the inner ear, a specialised population of these cells lines a structure called the stria vascularis inside the cochlea. This structure maintains the electrochemical environment that hair cells, the actual sensory receptors for sound, need to survive. When the W gene disrupts melanocyte migration, the stria vascularis does not form correctly. Without it, the hair cells degenerate in the first weeks of life. The result is permanent, irreversible deafness in one or both ears.
Why blue eyes are part of the picture
Eye colour in cats is also determined by melanocytes, specifically by how many pigment cells are present in the iris. A blue eye in a white cat is essentially an eye with very few or no melanocytes in its iris, the blue is not a pigment at all, but the way light scatters through tissue that lacks it. This is the same optical effect that makes the sky blue.
Because the same disruption to melanocyte migration that causes deafness also reduces pigment in the iris, blue eyes and deafness travel together statistically. A white cat with two blue eyes has a significantly higher chance of being deaf in both ears than a white cat with two eyes of other colours. A white cat with one blue eye and one eye of another colour, a condition called heterochromia, is more likely to be deaf on the blue-eyed side only. White cats with no blue eyes still carry some elevated risk compared to non-white cats, but the risk is considerably lower.
The numbers vary across studies, but a frequently cited figure from research led by veterinary geneticist George Strain at Louisiana State University puts the rate of deafness in white cats with two blue eyes at roughly 65 to 85 percent. White cats with one blue eye show unilateral deafness in a high proportion of cases. These are population-level figures, not a guarantee about any individual cat.
Odd-eyed cats and the one-sided question
An odd-eyed white cat, one blue eye, one green or gold, often hears perfectly well on the non-blue side and has no functional hearing on the blue side. A cat with unilateral deafness can be surprisingly hard to identify at home. It will respond to sound, locate you by the vibration of your footsteps, and startle at loud noises. The clues are subtler: difficulty locating the direction a sound came from, sleeping unusually deeply, not responding when approached from the deaf side.
A simple test used by breeders and vets is the BAER test, Brainstem Auditory Evoked Response. It measures the brain's electrical response to a click sound delivered to each ear separately, and it can confirm whether one or both ears are functional. It is the only reliable way to know for certain, because a cat with hearing in one ear compensates well enough to fool most informal tests.
Living with a deaf or partially deaf white cat
A cat that is deaf from birth does not experience its deafness as a loss. It has never had a reference point for sound, and it adapts its other senses accordingly. Deaf cats tend to be more visually alert, more sensitive to vibration, and more attuned to their owner's body language than hearing cats. They can live full, indoor lives.
The practical adjustments are straightforward. A deaf cat should be kept indoors or in a safely enclosed outdoor space, because it cannot hear approaching traffic, dogs, or other threats. Communication shifts to hand signals, which cats learn readily. Waking a deaf cat by touching it gently on the body rather than the head reduces the chance of a startled scratch. A gentle tap on the floor near the cat, or a deliberate footstep, gives it a moment's warning before contact.
The W gene connection is also why responsible breeders of breeds that commonly carry this gene, Turkish Van, Turkish Angora, and some lines of Maine Coon, now routinely BAER-test kittens before they go to new homes. If you are considering a white cat from a breeder, asking whether BAER testing has been done is a reasonable question.
The biology here is straightforward once you follow the cell. One gene, one disrupted migration route, two consequences that happen to be visible, a blue eye and a silent cochlea. The cat in front of you is not broken. It is just running on a different set of inputs than you assumed.