What Is Synesthesia?

Medically reviewed by Karen Foster, LPC
Updated April 24, 2024by BetterHelp Editorial Team

Synesthesia refers to a perceptual condition characterized by a blending of sensory experiences. For example, for people with synesthesia, specific words may have a flavor, days of the week may have different personalities, or the sound of music may be associated with colors. Synesthesia is not considered to be a disorder and usually causes no ill effects. Read on to learn more about this condition, its history, and some of the various forms of it that have been identified. 

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Synesthesia: A definition

The American Psychological Association defines synesthesia as “a condition in which stimulation of one sense generates a simultaneous sensation in another. These concomitant sensations are automatic (i.e., unintentional, uncontrollable, nonconscious, and efficient), vivid, and consistent over time”.

In other words, the individual doesn’t have to try to experience these perceptions, and the associations their brain makes (e.g., Wednesday and the color blue) are usually fixed throughout their lives. 

In most situations, synesthesia is not considered a disorder. Except in a few rare cases in which an individual complains of synesthesia overload, people with this manner of functioning are generally quite comfortable with it and live happy, creative, imaginative lives, stimulated by their extra sensation boost.

How common is synesthesia?

As one paper on the topic reports, synesthesia can occur “in response to drugs, sensory deprivation, or brain damage”, or it can be genetically inherited and experienced throughout a person’s life. Those with the genetic form of synesthesia are estimated to make up around 4% of the general population. However, it’s entirely possible that the actual incidence of the condition is higher because many people likely don’t know they have it. For example, a person might be surprised to discover that others aren’t able to pick out the letter “A” as quickly as they can in a letter-identification puzzle because, for others, the “A” does not stand out in the color red as it does for them.

Synesthesia throughout history

Cases of synesthesia have been reported throughout history. For example, a German poet and philosopher in 1772 mentioned that “through a sudden onset”, some people could “immediately associate with this sound that color”. In the mid-1800s, a French physician called this phenomenon “hyperchromatopsie (perception de trop de couleurs)”, referring to it as a “perception of too many colors”. Well-known Swiss psychiatrist Carl Jung mentioned it in one of his books in 1912, noting some people’s “perception of the tonal quality of colours and the chromatic quality of musical tones”. By the 1980s and 1990s, synesthesia had entered the mainstream both in terms of research and popular culture.


Types of synesthesia

Synesthesia describes the phenomenon where a person experiences a sensory perception that’s not normally related to the original sense through which they received the stimulus. Beyond this basic description, however, it can take many forms. Estimates on how many forms of this condition may exist range from 50 to 100 or more. Let’s take a look at just a few of these.

Grapheme-color synesthesia

Grapheme color is thought to be the most common form of synesthesia. People who have it generally see certain letters or numbers tinged with colors, or perceive them this way in their mind’s eye. Another variation of this type is "spatial sequence synesthesia”, in which a person sees the grapheme—a letter or number—as positioned differently in space. A seven may be large and close up while a four may seem to be very far away, for example.

Sound-color synesthesia

Another common form of synesthesia involves seeing colors or colorful shapes while hearing sounds. A person with sound-color synesthesia might see a sparkle of fireworks when a garbage can lid clatters, for instance, or they may see drifting blue smoke when a cat meows. Some people with sound-color synesthesia may only see colors with select, everyday sounds, while others may only experience it music.

Ordinal-linguistic personification (OLP)

With this variation of synesthesia, anything that comes in a sequence—such as days of the week, months of the year, letters, or numbers—may be associated in a person’s mind with distinct personalities, genders, and/or relationships. For example, the numbers one, two, and three might be perceived by a person with OLP as children who play together, or March and April might be sisters. Because this isn't necessarily a direct sensory association, though, there’s some debate as to whether it should be classified as a type of synesthesia. However, because it’s involuntary, many researchers feel it should be included in the category. 

Lexical-gustatory synesthesia

In this rare form of synesthesia, an individual will “experience phantom tastes when hearing, speaking, reading, or thinking about words”. For example, the word "desk" might taste like gingerbread, or “lantern” like icing. Sometimes, this type of synesthesia can be letter-associative. For example, the letter "C" might taste like chocolate.

Mirror-touch synesthesia (MTS)

Mirror-touch synesthesia refers to when a person experiences a phantom bodily sensation when they see another person experiencing one. For example, one well-known study had MTS synesthetes watch someone’s open palm be touched, and they reported feeling a sensation in the same part of their own palm. The reason for this perception is thought to have to do with certain somatosensory regions of the brain, which are active when anyone sees another person being touched. It may simply be that these networks are hyperactive in MTS synesthetes. 

When to seek help for synesthesia

Again, synesthesia is not generally considered to be a disorder and doesn’t usually cause any problems. As an expert quoted in the article linked above about hyperactive somatosensory networks puts it, “It’s just an interesting difference, like being double-jointed”. However, there are a few instances in which it may be cause for concern. 

First, genetic synesthesia is usually a life-long attribute that first manifests in childhood. If you suddenly begin to acquire synesthesia as an adult, it’s generally recommended that you consult with a doctor. Grapheme-color, sound-color, and number-form synesthesia all manifest as visuals that could be early warning signs of a serious medical condition, since head trauma, brain tumors, certain infections, migraines, seizures, cerebral strokes, and epilepsy can all cause symptoms of synesthesia.

Secondly, some people find the additional sensory perceptions they experience with synesthesia to be overwhelming. This can be especially true for those on the autism spectrum, who may experience sensory overwhelm more easily and may also be more likely to have synesthesia. Others may experience self-esteem issues or anxiety around the fact that they perceive the world differently than others. In cases like these, therapy may be helpful. A therapist can help an individual learn to manage the overwhelm they may feel because of synesthesia, and they can also assist them in accepting this unique difference in themselves over time. 

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Synesthesia refers to a phenomenon where a person has one sensory experience after perceiving a stimulus through another sense, such as seeing colors associated with numbers. It’s not considered to be a disorder or even problematic unless it comes on suddenly in adulthood or causes frequent sensory overwhelm or self-esteem issues.
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