What Is Synesthesia?

Synesthesia is an interesting brain condition in which one sensation triggers another. And both sensations are experienced at the same time. It comes from the Greek words for “union of the senses.” Synesthesia is not a disease or mental disorder. It’s just a different way of experiencing the world around you.

It’s unclear how many people have synesthesia. In the past, scientists thought that 1 in 2000 people had synesthesia. But it may be more common than that. In this article, we discuss the different types of synesthesia and how to tell if you or someone you know has it.

What’s the definition of synesthesia?

Synesthesia means experiencing two sensations — like seeing and hearing — at the same time. You might be thinking: “I see and hear things together all the time. What’s the big deal?” The difference with synesthesia is that one sensation (like hearing music) leads to an automatic and involuntary experience of the other sensation (like seeing colors). People who have synesthesia are called “synesthetes.”

How many types of synesthesia are there? What are some examples of synesthesia?

Synesthesia can occur between any of the five senses (sound, taste, sight, smell, and touch). There are many different types of synesthesia. Some are very rare and some are more common. Examples include: 

• Grapheme-color synesthesia: Seeing certain letters or numbers (graphemes) leads to seeing colors. For example, the letter “B” might appear orange, but it’s just black print. This is one of the most common types of synesthesia.

• Chromesthesia: Hearing sounds leads to seeing colors. For example, hearing a certain musical note might cause you to see the color green. 

• Spatial sequence (visio-spatial synesthesia): This one is a little more abstract. People with this type of synesthesia see sequences like months, numbers, or letters arranged in space around them. For example, thinking about a calendar might cause you to see months of the year around you in a circle. 

• Auditory-tactile synesthesia: Hearing sounds leads to specific sensations in parts of the body. It’s as if you’re being touched, but nothing is touching you. For example, hearing heavy metal music might feel like pins and needles on your legs.

• Lexical-gustatory (sound-gustatory): Thinking about, hearing, or reading certain words leads to a specific taste in the mouth. For example, hearing the word “table” might cause you to taste peanut butter. Although, you aren’t eating any. This is very rare.

• Mirror-touch synesthesia: Seeing someone experience a feeling, like pain, causes you to feel the same thing, even if nothing is touching you. For example, watching someone burn their hand on the stove might cause a burning sensation in your own hand. How intense the sensation is varies from person to person. This is also very rare.

What causes synesthesia?

Humans have known that synesthesia exists for more than 100 years. But it wasn’t until the 2000s that we started to understand why it happens.

Scientists are still studying the exact cause of synesthesia. So far, we know that synesthesia is somewhat genetic. If one of your birth parents has synesthesia, you are more likely to have it as well. 

Cross-activation in nearby areas of the brain also contributes to synesthesia. In other words, when certain brain cells are activated, neighboring cells accidentally get turned on, too. This causes two sensations at once.

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Of note, psychedelic drugs, like LSD (“acid”) and psilocybin (“mushrooms”), can cause synesthesia while under the influence of their effects. This type of synesthesia stops once the drugs are out of your system.

How do I know if I have synesthesia?

Scientists have developed a test called the “synesthesia battery” to identify people with synesthesia. The test is available for free online. It includes a questionnaire as well as many computer-based tests that can figure out if you’re experiencing two sensations at once. The tests are repeated over time to make sure responses are consistent. For example, a person who truly has synesthesia will report seeing the same color with the same letter — like red with the letter “A” — every time. 

Does synesthesia need treatment?

No. Synesthesia isn’t a disease. In fact, a lot of people consider synesthesia to be helpful, since it enhances the way they experience their surroundings. 

Is synesthesia a type of autism?

No. Autism is a condition that changes how people interact with others and the world around them. It may be tough for people with autism to make eye contact or understand how other people feel (empathize). People with autism may have decreased connections between nerves in certain parts of the brain. On the other hand, people with synesthesia may have increased connections in the brain (cross-activation) that lead to feeling more than one sensation at the same time.

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Written by:

Samantha C. Shapiro, MD

Samantha Shapiro, MD, is a board-certified rheumatologist and internist with expertise in autoimmune and inflammatory conditions. She founded the division of rheumatology at Dell Medical School at The University of Texas at Austin.

Edited by:

Mandy Armitage, MD

Mandy Armitage, MD, has combined clinical medicine with her passion for education and content development for many years. She served as medical director for the health technology companies HealthLoop (now Get Well) and Doximity.

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